GOLF CLUB HEAD

Abstract

A golf club head includes a face portion including a striking face, a crown portion including a crown surface, a sole portion including a sole surface, and a hosel portion including a protruding portion that protrudes from the crown surface. The hosel portion includes a single upper end surface that is a substantially flat surface, and a plurality of shaft receiving holes formed on the upper end surface. The shaft receiving holes include a first shaft receiving hole and a second shaft receiving hole. The golf club head also includes a cover member that covers at least one of the shaft receiving holes which is not to have a shaft inserted.

Claims

1. A golf club head comprising: a face portion including a striking face, a crown portion including a crown surface, a sole portion including a sole surface, and a hosel portion including a protruding portion that protrudes from the crown surface, wherein the hosel portion includes a single upper end surface that is a substantially flat surface, and a plurality of shaft receiving holes formed on the upper end surface, the shaft receiving holes include a first shaft receiving hole and a second shaft receiving hole, and the golf club head further includes a cover member that covers at least one of the shaft receiving holes which is not to have a shaft inserted.

2. The golf club head according to claim 1, wherein the first shaft receiving hole is located on a face side relative to the second shaft receiving hole.

3. The golf club head according to claim 2, wherein a center line of the second shaft receiving hole is inclined toward the face side compared to a center line of the first shaft receiving hole.

4. The golf club head according to claim 2, wherein a center line of the second shaft receiving hole is inclined toward a toe side compared to a center line of the first shaft receiving hole.

5. The golf club head according to claim 1, wherein the shaft receiving holes each have a stepped portion in a vicinity of the upper end surface, and the golf club head is configured such that a sleeve attached to a tip portion of the shaft is fixed to the hosel portion while engaging with the stepped portion of one of the shaft receiving holes.

6. The golf club head according to claim 1, wherein the upper end surface of the hosel portion extends along a heel-side contour of the crown surface.

7. The golf club head according to claim 6, wherein the golf club head further includes a crown contour protruding portion that extends along the heel-side contour of the crown surface from the upper end surface of the hosel portion toward a back side.

8. The golf club head according to claim 1, wherein the upper end surface has a radius of curvature in a cross section of greater than or equal to 152 mm.

9. The golf club head according to claim 1, wherein the upper end surface includes an opening line of the first shaft receiving hole, an opening line of the second shaft receiving hole, and a part located between the first shaft receiving hole and the second shaft receiving hole.

10. The golf club head according to claim 1, wherein the cover member includes a fixed portion having a through hole, and a cover portion that covers at least one of the shaft receiving holes which is not to have the shaft inserted, when the shaft is inserted into the first shaft receiving hole, the fixed portion is fixed to the first shaft receiving hole, and the cover portion covers the second shaft receiving hole, and when the shaft is inserted into the second shaft receiving hole, the fixed portion is fixed to the second shaft receiving hole and the cover portion covers the first shaft receiving hole.

11. The golf club head according to claim 2, wherein a distance in a face-back direction between a center of the first shaft receiving hole and a center of the second shaft receiving hole is greater than or equal to 15 mm and less than or equal to 25 mm.

12. A golf club head comprising: a face portion including a striking face, a crown portion including a crown surface, a sole portion including a sole surface, and a hosel portion including a protruding portion that protrudes from the crown surface, wherein the hosel portion includes a first shaft receiving hole and a second shaft receiving hole, and the golf club head further includes a cover member that covers either the first shaft receiving hole or the second shaft receiving hole which is not to have a shaft inserted.

13. The golf club head according to claim 12, wherein the first shaft receiving hole is located on a face side relative to the second shaft receiving hole.

14. The golf club head according to claim 13, wherein a center line of the second shaft receiving hole is inclined toward the face side compared to a center line of the first shaft receiving hole.

15. The golf club head according to claim 13, wherein a center line of the second shaft receiving hole is inclined toward a toe side compared to a center line of the first shaft receiving hole.

16. The golf club head according to claim 12, wherein the cover member includes a fixed portion having a through hole, and a cover portion that covers either the first shaft receiving hole or the second shaft receiving hole which is not to have the shaft inserted, when the shaft is inserted into the first shaft receiving hole, the fixed portion is fixed to the first shaft receiving hole, and the cover portion covers the second shaft receiving hole, and when the shaft is inserted into the second shaft receiving hole, the fixed portion is fixed to the second shaft receiving hole and the cover portion covers the first shaft receiving hole.

17. The golf club head according to claim 13, wherein a distance in a face-back direction between a center of the first shaft receiving hole and a center of the second shaft receiving hole is greater than or equal to 15 mm and less than or equal to 25 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a plan view of a golf club head according to a first embodiment as viewed from an upper side;

[0008] FIG. 2 is a front view of the head of the first embodiment as viewed from a face side;

[0009] FIG. 3 is a back view of the head of the first embodiment as viewed from a back side;

[0010] FIG. 4 is a side view of the head of the first embodiment as viewed from a heel side;

[0011] FIG. 5 shows the head of the first embodiment as viewed from a position facing un upper end surface of a hosel portion;

[0012] FIG. 6 is a perspective view of the head of the first embodiment;

[0013] FIG. 7 shows the head of the first embodiment as viewed from the heel lower side;

[0014] FIG. 8 is a perspective view showing the head of the first embodiment with a shaft inserted into a first shaft receiving hole of the head;

[0015] FIG. 9 is a perspective view showing the head of the first embodiment with a shaft inserted into a second shaft receiving hole of the head;

[0016] FIG. 10 shows a head according to a second embodiment as viewed from a position facing un upper end surface of a hosel portion;

[0017] FIG. 11 is a plan view of a head in which the upper end surface of the hosel portion and the surface of a crown contour protruding portion have the same color, which is different from the color of the other part of the crown surface;

[0018] FIG. 12 is a cross-sectional view taken along line A-A in FIG. 8;

[0019] FIG. 13 is a cross-sectional view corresponding to FIG. 12, and shows a modification example of a cover member;

[0020] FIG. 14 is a cross-sectional view corresponding to FIG. 12, and shows another modification example of the cover member;

[0021] FIG. 15 is a cross-sectional view showing still another modification example of the cover member;

[0022] FIG. 16A is a perspective view of the cover member shown in FIG. 15, and FIG. 16B is a perspective view of the cover member, which is turned upside down from the state shown in FIG. 16A;

[0023] FIG. 17A shows a first usage state of the cover member shown in FIG. 15, FIG. 16A and FIG. 16B, and FIG. 17B shows a second usage state of the cover member; and

[0024] FIG. 18 is a conceptual diagram for illustrating a reference state.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, the present disclosure will be described in detail according to preferred embodiments with appropriate references to the accompanying drawings. In the following embodiments, the same or common elements are denoted by the same reference symbols, and duplicated explanations will be omitted as appropriate.

[0026] The terms, reference state, reference perpendicular plane, toe-heel direction, face-back direction, up-down direction, planar view, and face center are defined as follows in the present disclosure.

[0027] The reference state is a state where a head is placed at a predetermined lie angle on a ground plane HP. As shown in FIG. 18, in the reference state, a shaft axis line Z lies on (is contained in) a plane VP that is perpendicular to the ground plane HP. The shaft axis line Z refers to the center line of a shaft. The plane VP is referred to as the reference perpendicular plane. The predetermined lie angle is shown in a product catalog, for example. When the head has a plurality of shaft receiving holes, the shaft axis line Z in the reference state is determined based on a shaft receiving hole that is located at the face-most and heel-most position.

[0028] There has been known a club in which its loft angle, lie angle and face angle can be adjusted by, for example, changing a rotational position of a sleeve provided at a tip portion of a shaft. In such a club, the sleeve can be detachably fixed to the head with a fixing means such as a screw. For this reason, in this club, the shaft is attachable to and detachable from the head. In a club having such an attachable/detachable mechanism, the face angle and the loft angle can be set to neutral and the lie angle can be set to maximum in the reference state. The term neutral means the center of the range of adjustment.

[0029] In the reference state, the face angle is 0. That is, in a planer view of the head as viewed from above, a tangent line to the head at its face center on a striking face is set to be parallel to the toe-heel direction. The definitions of the face center and the toe-heel direction are explained below.

[0030] In the present disclosure, the toe-heel direction is the direction of an intersection line NL between the reference perpendicular plane VP and the ground plane HP (see FIG. 18).

[0031] In the present disclosure, the face-back direction is a direction that is perpendicular to the toe-heel direction and is parallel to the ground plane HP.

[0032] In the present disclosure, the up-down direction is a direction that is perpendicular to the toe-heel direction and is perpendicular to the face-back direction. In other words, the up-down direction in the present disclosure is a direction perpendicular to the ground plane HP.

[0033] In the present disclosure, the planar view refers to the planar view of a hosel portion. The planar view means a projected figure that is obtained by projecting a head onto a flat plane perpendicular to the center line of a shaft receiving hole located at the face-most position among a plurality of shaft receiving holes. FIG. 5 explained below is an example of the projected figure.

[0034] In the present disclosure, the face center is determined in the following manner. First, a point Pr is selected roughly at the center of a striking face in the up-down direction and the toe-heel direction. Next, a plane that passes through the point Pr, extends in the direction of a line normal to the striking face at the point Pr, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is determined. Next, a plane that passes through the midpoint Px, extends in the direction of a line normal to the striking face at the midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is determined. Next, a plane that passes through the midpoint Py, extends in the direction of a line normal to the striking face at the midpoint Py, and is parallel to the toe-heel direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Px of this intersection line is newly determined. Next, a plane that passes through this newly-determined midpoint Px, extends in the direction of a line normal to the striking face at this midpoint Px, and is parallel to the up-down direction is determined. An intersection line between this plane and the striking face is drawn, and a midpoint Py of this intersection line is newly determined. By repeating the above-described steps, points Px and Py are sequentially determined. In the course of repeating these steps, when the distance between a newly-determined midpoint Py and a midpoint Py determined in the immediately preceding step first becomes less than or equal to 0.5 mm, the newly-determined midpoint Py (the midpoint Py determined last) is defined as the face center.

[0035] FIG. 1 is a plan view of a head 4 according to a first embodiment of the present disclosure as viewed from the upper side. FIG. 2 is a front view of the head 4. FIG. 2 shows the head 4 which is in the reference state as viewed from the face side. FIG. 3 is a back view of the head 4 as viewed from the back side. FIG. 4 is a side view of the head 4 as viewed from the heel side. FIG. 5 shows the head 4 as viewed along the extended center line of a first shaft receiving hole. FIG. 5 is a planar view of a hosel portion. FIG. 6 is a perspective view of the head 4.

[0036] As shown in FIG. 1 to FIG. 6, the head 4 includes a face portion 10, a crown portion 12, a sole portion 14, and a hosel portion 16. The face portion 10 includes a striking face 10a. The striking face 10a is the outer surface of the face portion 10. The striking face 10a is also simply referred to as a face. The striking face 10a includes a face center Fc (see FIG. 1). The crown portion 12 includes a crown surface 12a. The crown surface 12a is the outer surface of the crown portion 12. The sole portion 14 includes a sole surface 14a. The sole surface 14a is the outer surface of the sole portion 14.

[0037] The head 4 is a wood type head. The head 4 may be a hybrid type head. The head 4 may be an iron type head. The head 4 may be a putter type head. From the viewpoint of having an area for forming a plurality of shaft receiving holes, the head 4 preferably has a large projected area as viewed from above. From this viewpoint, the head 4 is preferably a wood type head or a hybrid type head, and more preferably a wood type head. Examples of the wood type head include a driver head and a fairway wood type head. The head 4 of the present embodiment is a driver head. The volume of the head 4 can be greater than or equal to 300 cm.sup.3, further can be greater than or equal to 400 cm.sup.3, and still further can be greater than or equal to 420 cm.sup.3.

[0038] Examples of a preferable material for the head 4 include metals and fiber reinforced plastics. Examples of the metals include titanium alloys, pure titanium, stainless steel, maraging steel, and soft iron. Examples of the fiber reinforced plastics include carbon fiber reinforced plastics. The head 4 may be a composite head including a portion made of a metal and a portion made of a fiber reinforced plastic.

[0039] The hosel portion 16 includes a protruding portion 16a that protrudes from the crown surface 12a. The protruding portion 16a constitutes an upper end part of the hosel portion 16. A hosel portion of a normal head includes a protruding portion having a cylindrical shape, and the upper end surface of this cylinder is the upper end surface of the hosel portion. On the other hand, the hosel portion 16 of the present embodiment does not include a cylindrical protruding portion. The protruding portion 16a has a substantially quadrilateral shape in the planar view.

[0040] The hosel portion 16 includes a single upper end surface 16b that is a substantially flat surface. The upper end surface 16b of the hosel portion 16 is the upper surface of the protruding portion 16a. The entirety of the upper end surface 16b extends with no step. The upper end surface 16b may be a flat surface, or may be a curved surface having a small curvature. The curved surface having a small curvature may be a convex curved surface, a concave curved surface, or a curved surface having a varying curvature. The term substantially flat surface means that the radius of curvature of the upper end surface 16b in a cross section is preferably greater than or equal to 152 mm, more preferably greater than or equal to 203 mm, and still more preferably greater than or equal to 256 mm. This radius of curvature is measured in a cross section taken in a direction in which the radius of curvature is at the minimum.

[0041] The hosel portion 16 includes a plurality of shaft receiving holes h1 and h2. In the present embodiment, the number of the shaft receiving holes is two. The number of the shaft receiving holes may be greater than or equal to three. The greater the number of the shaft receiving holes, the more adjustability can be achieved by changing the position of the shaft. On the other hand, when the number of the shaft receiving holes is excessively large, the weight of the hosel portion increases significantly, which can reduce the design flexibility of the head. From this viewpoint, the number of the shaft receiving holes is preferably greater than or equal to 2 and less than or equal to 4, more preferably greater than or equal to 2 and less than or equal to 3, and still more preferably 2.

[0042] The hosel portion 16 includes a first shaft receiving hole h1 and a second shaft receiving hole h2 as the plurality of shaft receiving holes. The first shaft receiving hole h1 and the second shaft receiving hole h2 are both located on the upper end surface 16b, which is a single, substantially flat surface. All the shaft receiving holes h1 and h2 are located on the upper end surface 16b, which is a single, substantially flat surface.

[0043] The first shaft receiving hole h1 and the second shaft receiving hole h2 are spaced apart from each other on the upper end surface 16b. The upper end surface 16b includes a part located between the first shaft receiving hole h1 and the second shaft receiving hole h2.

[0044] The first shaft receiving hole h1 is located on the face side relative to the second shaft receiving hole h2. The position of the first shaft receiving hole h1 can be determined as the position of the center of the first shaft receiving hole h1. The center of the first shaft receiving hole h1 can refer to the geometric center of a figure outlined by an opening line k1 on the upper end surface 16b. Similarly, the position of the second shaft receiving hole h2 can be determined as the position of the center of the second shaft receiving hole h2. The center of the second shaft receiving hole h2 can refer to the geometric center of a figure outlined by an opening line k2 on the upper end surface 16b. These centers are determined in the planar view (FIG. 5) of the hosel portion 16. In the planar view of the hosel portion 16, the center of the first shaft receiving hole h1 is located on the face side relative to the center of the second shaft receiving hole h2.

[0045] FIG. 7 shows the head 4 as viewed from the heel lower side. FIG. 8 and FIG. 9 are perspective views showing a golf club in which a shaft 6 is attached to the head 4 so that the golf club is ready for use. The shaft 6 with a sleeve 8 attached to the tip portion of the shaft 6 is inserted into the shaft receiving hole h1 or h2. The sleeve 8 is fixed to the shaft receiving hole h1 or h2 using a coupling member, such as a screw, as discussed below. The shaft 6 is inserted into and fixed to either the shaft receiving hole h1 or h2 through the sleeve 8. The sleeve 8 is attachable to all the shaft receiving holes h1 and h2. All the shaft receiving holes have the same structure. Although the positions and orientations of the shaft receiving holes can differ from each other, their structures designed for coupling with the sleeve 8 are identical. Note that sleeve 8 is hereinafter also referred to as coupling sleeve 8.

[0046] As described above, the head 4 includes the shaft receiving holes h1 and h2 for coupling with the shaft 6 to which the coupling sleeve 8 is attached. The coupling between the shaft 6 and the shaft receiving hole h1 or h2 may be achieved by adhesion using an adhesive. From the viewpoint of easy detachment of the shaft from one shaft receiving hole and easy attachment of the shaft to another shaft receiving hole, the coupling between the shaft 6 and the shaft receiving hole h1 or h2 is preferably achieved using the coupling sleeve 8. That is, the coupling between the shaft 6 and the shaft receiving hole h1 or h2 is preferably achieved by an attachable/detachable mechanism in which the shaft 6 with the sleeve 8 attached is attachable to and detachable from the shaft receiving holes h1 and h2. Such an attachable/detachable mechanism is well known, and the structure of the sleeve 8 and the structure of the shaft receiving hole to which the sleeve 8 is attachable is also well known.

[0047] FIG. 8 shows the head 4 with the shaft 6 inserted into the first shaft receiving hole h1. In this state, the second shaft receiving hole h2, which does not have the shaft 6 inserted, is covered by a cover member 18. FIG. 9 shows the head 4 with the shaft 6 inserted into the second shaft receiving hole h2. In this state, the first shaft receiving hole h1, which does not have the shaft 6 inserted, is covered by the cover member 18.

[0048] As described above, the head 4 includes the cover member 18 that covers one of the shaft receiving holes h1 and h2 which does not have the shaft 6 inserted. Hereinafter, a shaft receiving hole which does not have the shaft 6 inserted is also referred to as an unused shaft receiving hole. The cover member 18 can be used in common for all the shaft receiving holes. That is, the cover member 18 can cover the first shaft receiving hole h1, and also can cover the second shaft receiving hole h2. In the present embodiment, the number of the cover member 18 is one. The number of the cover member(s) 18 can be one less than the number of the shaft receiving holes. For example, when the number of the shaft receiving holes is three, the number of the cover members 18 can be two. Note that cover members different from each other can be used for respective shaft receiving holes.

[0049] The inside of the unused shaft receiving hole is concealed by covering it with the cover member 18. The unused shaft receiving hole becomes less conspicuous when covered by the cover member 18. When the unused shaft receiving hole is covered by the cover member 18, an exposed surface (upper surface) 18a of the cover member 18 is substantially flush with the upper end surface 16b of the hosel portion 16. In the present embodiment, the exposed surface 18a is a flat surface. The height of a step between the exposed surface 18a and the upper end surface 16b can be less than or equal to 2.0 mm, further can be less than or equal to 1.5 mm, and still further can be less than or equal to 1.0 mm. A substantially common flat plane may be formed by the exposed surface 18a and the upper end surface 16b. The substantially common flat plane refers to a single virtual flat plane that has a distance of less than or equal to 2.0 mm from all points on the exposed surface 18a and the upper end surface 16b. This distance is measured in the direction perpendicular to the virtual flat plane. The cover member 18 is not conspicuous.

[0050] As shown in FIG. 7, in the present embodiment, the center line z2 of the second shaft receiving hole h2 is inclined toward the face side compared to the center line z1 of the first shaft receiving hole h1. In other words, the center line z2 of the second shaft receiving hole h2 is inclined to increase the real loft angle compared to the center line z1 of the first shaft receiving hole h1. The real loft angle based on the center line z2 of the second shaft receiving hole h2 is greater than the real loft angle based on the center line z1 of the first shaft receiving hole h1.

[0051] The center line z1 of the first shaft receiving hole h1 can coincide with the shaft axis line Z when the shaft 6 is inserted into the first shaft receiving hole h1 of the head 4. Some golf clubs have an adjustment mechanism that enables the adjustment of loft angle, lie angle, and face angle by changing the rotational position of the sleeve 8. In this case, the center line z1 may not coincide with the shaft axis line Z. However, the real loft angle based on the center line z1 can coincide with the real loft angle based on the shaft axis line Z by adjusting the loft angle to neutral.

[0052] Similarly, the center line z2 of the second shaft receiving hole h2 can coincide with the shaft axis line Z when the shaft 6 is inserted into the second shaft receiving hole h2 of the head 4. Some golf clubs have an adjustment mechanism that enables the adjustment of loft angle, lie angle, and face angle by changing the rotational position of the sleeve 8. In this case, the center line z2 may not coincide with the shaft axis line Z. However, the real loft angle based on the center line z2 can coincide with the real loft angle based on the shaft axis line Z by adjusting the loft angle to neutral.

[0053] As shown in FIG. 2, in the present embodiment, the center line z2 of the second shaft receiving hole h2 is inclined toward the toe side compared to the center line z1 of the first shaft receiving hole h1. In other words, the center line z2 of the second shaft receiving hole h2 is inclined to increase the lie angle compared to the center line z1 of the first shaft receiving hole h1. The lie angle when the shaft 6 is inserted into the second shaft receiving hole h2 is greater than the lie angle when the shaft 6 is inserted into the first shaft receiving hole h1.

[0054] As described above, when the golf club has an adjustment mechanism that enables the adjustment of loft angle, lie angle, and face angle by changing the rotational position of the sleeve 8, the center line z1 may not coincide with the shaft axis line Z. In this case, the lie angle based on the center line z1 can coincide with the lie angle based on the shaft axis line Z by adjusting the lie angle to neutral. Similarly, the lie angle based on the center line z2 can coincide with the lie angle based on the shaft axis line Z by adjusting the lie angle to neutral.

[0055] The head 4 includes a crown contour protruding portion 20. The crown contour protruding portion 20 is continuous with the upper end surface 16b of the hosel portion 16. The crown contour protruding portion 20 extends along a heel-side contour (contour line of a heel-side part) of the crown surface 12a, starting from the upper end surface 16b. The crown contour protruding portion 20 protrudes from the crown surface 12a. The crown contour protruding portion 20 extends toward the back side from the back-side edge of the upper end surface 16b. The crown contour protruding portion 20 terminates at a position on the face side relative to the back-most point b1 of the head 4 (see FIG. 1). The crown contour protruding portion 20 includes a width decreasing portion 20a having a width in the toe-heel direction that continuously decreases toward the back side (hereinafter, a width in the toe-heel direction is also referred to as toe-heel directional width). The width decreasing portion 20a extends to reach the back-side end point 20b of the crown contour protruding portion 20. The maximum value of the toe-heel directional width of the crown contour protruding portion 20 is smaller than the maximum value of the toe-heel directional width of the upper end surface 16b. The upper surface of the crown contour protruding portion 20 is continuous with the upper end surface 16b of the hosel portion 16, with no step.

[0056] As shown in the enlarged portion of FIG. 6, each of the shaft receiving holes h1 and h2 has a stepped portion 22 in the vicinity of the upper end surface 16b. Each stepped portion 22 includes a step surface 22a having an annular shape and an erecting surface 22b whose lower edge coincides with the outer edge of the step surface 22a. The erecting surface 22b forms the inner circumferential surface of each of the shaft receiving holes h1 and h2. The step surface 22a is formed such that the inner diameter of each of the shaft receiving holes h1 and h2 varies. The step surface 22a of each of the shaft receiving holes h1 and h2 may form a flat surface perpendicular to the center line z1 for the step surface 22a of the shaft receiving hole h1, and perpendicular to the center line z2 for the step surface 22a of the shaft receiving hole h2. Alternatively, the step surface 22a of each of the shaft receiving holes h1 and h2 may form a conically recessed surface with its center line coinciding with the center line z1 for the step surface 22a of the shaft receiving hole h1, and coinciding with the center line z2 for the step surface 22a of the shaft receiving hole h2. The sleeve 8 is fixed to the hosel portion 16 while engaging with the stepped portion 22 of one of the shaft receiving holes h1 and h2.

[0057] In the present embodiment, the stepped portion 22 extends throughout the entire inner circumference (360) of each of the shaft receiving holes h1 and h2. Alternatively, the stepped portion 22 may be situated only on a part of the inner circumference of each of the shaft receiving holes h1 and h2. For example, the stepped portion 22 may have gaps arranged at equal intervals around the inner circumference of each of the shaft receiving holes h1 and h2.

[0058] Each stepped portion 22 is located in the vicinity of the upper end surface 16b. A shortest distance between the upper end surface 16b and the step surface 22a of each stepped portion 22 can be less than or equal to 2 mm, further can be less than or equal to 1.0 mm, and still further can be less than or equal to 0.5 mm. This shortest distance is measured along the center line z1 for the step surface 22a of the shaft receiving hole h1, and along the center line z2 for the step surface 22a of the shaft receiving hole h2.

[0059] FIG. 10 shows a head 24 according to a second embodiment. Similar to FIG. 5, FIG. 10 shows the head 24 as viewed along the extended center line of the first shaft receiving hole.

[0060] In the head 24, the toe-heel directional position (i.e., position in the toe-heel direction) of the first shaft receiving hole h1 differs from the toe-heel directional position of the second shaft receiving hole h2. The second shaft receiving hole h2 is positioned on the toe side relative to the first shaft receiving hole h1. Additionally, the first shaft receiving hole h1 is positioned on the face side relative to the second shaft receiving hole h2. Except for this difference, the head 24 has the same configuration as the head 4.

[0061] FIG. 11 is a plan view of a head 26 according to a third embodiment. Except for the colors of the hosel portion 16 and the crown contour protruding portion 20, the head 26 has the same configuration as the head 4.

[0062] In the plan view (FIG. 11) of the head 26 as viewed from the upper side, the color of the hosel portion 16 is the same as the color of the crown contour protruding portion 20. The color of the upper end surface 16b is the same as the color of the surface of the crown contour protruding portion 20. Additionally, in this plan view, the color of the cover member 18 is the same as the color of the hosel portion 16. The color of the exposed surface 18a of the cover member 18 is the same as the color of the upper end surface 16b. Furthermore, in this plan view, the color of the sleeve 8 attached to the head 26 is the same as the color of the hosel portion 16. The color of the exposed surface of the sleeve 8 is the same as the color of the upper end surface 16b.

[0063] In the plan view of the head 26 as viewed from the upper side, the color of the hosel portion 16 differs from the color of the crown surface 12a excluding the hosel portion 16. The color of the crown contour protruding portion 20 differs from the color of the crown surface 12a excluding the hosel portion 16. As shown in FIG. 11, the colors of the hosel portion 16 and the crown contour protruding portion 20 in the plan view may be black, for example. This black may be specified by the following conditions in the Munsell color system: H (Hue)=66 to 50; S (Saturation)=27 to 1%; and V (Value)30 to 4%. As shown in FIG. 11, in the plan view, the color of the crown surface 12a excluding the hosel portion 16 may be white, for example. This white may be specified by the following conditions in the Munsell color system: H (Hue)=20 to 13; S (Saturation)=4 to 1%; and V (Value)=96 to 90%.

[0064] The sameness of colors may be determined by color difference E. For example, when the color difference E is less than or equal to 20.0, the compared colors may be determined as the same. Conversely, when the color difference E is greater than 20.0, the compared colors may be determined as different. The color difference E can be calculated using values obtained by measuring colors of two regions with a commercially available color measuring device (for example, CR-400 manufactured by Konica Minolta, Inc.). The color difference E can be obtained by comparing values digitized based on CIE1976 (L*a*b*) color space specified in JIS Z 8729. Specifically, when two regions have a difference in L* values of L*, a difference in a* values of a*, and a difference in b* values of b*, the color difference E can be calculated using the following formula: E=[(L*).sup.2+(a*).sup.2+(b*).sup.2].sup.1/2.

[0065] FIG. 12 is a cross-sectional view taken along line A-A in FIG. 8. FIG. 12 shows a cross section taken along the center line z2 of the shaft receiving hole h2 covered by the cover member 18. Note that although the cover member 18 is attached to the second shaft receiving hole h2 in FIG. 12, all the shaft receiving holes have the same structure. Accordingly, the cover member 18 can also be attached to the first shaft receiving hole h1 as explained above.

[0066] In the embodiment shown in FIG. 12, a cover member 181 that has a disc-shape as a whole is used as the cover member 18. The cover member 181 engages with the stepped portion 22. The cover member 181 is fitted into the stepped portion 22. A screw 30 is tightened into the cover member 181 from the lower side. The screw 30 is screwed into a female screw hole 28 formed on the lower surface of the cover member 181. Except for the length of a shaft portion 30a of the screw 30, the screw 30 has the same configuration as a screw 32 (described later) provided for fixing the sleeve 8. The screw 30 is retained by the head body utilizing the fixing structure for the sleeve 8. The shaft portion 30a of the screw 30 is longer than the shaft portion of the screw 32.

[0067] The shaft receiving hole h2 has a lower-side opening 34 and a flange 36 that forms the lower-side opening 34. The screw 30 is inserted such that the shaft portion 30a passes through the lower-side opening 34 from the sole side, and a head portion 30b of the screw 30 is retained by the flange 36. A washer 37 is disposed between the head portion 30b and the flange 36. A male screw 30c formed on the shaft portion 30a is screw-connected to the female screw hole 28. The structure for fixing the cover member 181 with the screw 30 is the same as the structure used for fixing the sleeve 8 with the screw 32. As described above, the cover member 181 is fixed to the shaft receiving hole h2 by being fastened with a screw from the lower side.

[0068] FIG. 13 shows another example of the cover member 18. In the embodiment shown in FIG. 13, a cover member 182 that has a disc-shape as a whole is used as the cover member 18. The cover member 182 engages with the stepped portion 22. The cover member 182 has a male screw 38 on its outer circumferential surface. On the other hand, a female screw 40 is formed on the erecting surface 22b of the stepped portion 22. The male screw 38 is screw-connected to the female screw 40. Thus, the cover member 182 is fixed to the shaft receiving hole h2 by screw connection. In FIG. 13, the screw 32 used for fixing the sleeve 8 is attached to the lower-side opening 34. However, the screw 32 does not have to be present.

[0069] FIG. 14 shows still another example of the cover member 18. In the embodiment shown in FIG. 14, a cover member 183 having a structure similar to the sleeve 8 is used as the cover member 18. The cover member 183 includes an engaging stepped portion 42 that engages with the stepped portion 22. The lower part of the cover member 183 has a female screw hole 44 that opens toward the lower side. The female screw hole 44 is screw-connected to the screw 32 inserted into the lower-side opening 34 from the sole side. The screw 32 is inserted such that its shaft portion 32a passes through the lower-side opening 34 from the sole side, and a head portion 32b of the screw 32 is retained by the flange 36. A male screw 32c formed on the shaft portion 32a is screw-connected to the female screw hole 44. The screw 32 is identical to the screw 32 used for fixing the sleeve 8. The engaging stepped portion 42 is identical to that of the sleeve 8. The female screw hole 44 is identical to that of the sleeve 8. As described above, the cover member 183 is fixed to the shaft receiving hole h2 by being fastened with a screw from the lower side.

[0070] FIG. 15 shows yet another example of the cover member 18. In the embodiment shown in FIG. 15, a cover member 184 is used as the cover member 18. The cover member 184 is fixed by the sleeve 8 attached to the shaft receiving hole h1 adjacent to the shaft receiving hole h2 covered by the cover member 184. FIG. 15 is a cross-sectional view taken along the center line z1 of the shaft receiving hole h1 and the center line z2 of the shaft receiving hole h2.

[0071] In FIG. 15, the shaft 6 fixed to the sleeve 8 is inserted into the first shaft receiving hole h1. In this case, the cover member 184 is fixed by being sandwiched between the sleeve 8 and the shaft receiving hole h1, and covers the shaft receiving hole h2. Although not shown in drawings, when the shaft 6 is inserted into the second shaft receiving hole h2, the cover member 184 is fixed by being sandwiched between the sleeve 8 and the shaft receiving hole h2, and covers the shaft receiving hole h1. In the present embodiment, the cover member 184 is fixed by utilizing the fixation of the sleeve 8 to the adjacent shaft receiving hole.

[0072] The sleeve 8 includes a shaft hole 46 into which the shaft 6 is inserted and adhered, a female screw hole 44 that is formed on the lower side relative to the shaft hole 46 and opens toward the lower side, an engaging stepped portion 42 formed on the outer circumferential surface of the sleeve 8, and a rotation prevention portion 48 that engages with the shaft receiving hole h1 or h2 to prevent the sleeve 8 from rotating relative to the shaft receiving hole h1 or h2.

[0073] FIG. 16A is a perspective view of the cover member 184 as viewed from the upper side. FIG. 16B is a perspective view of the cover member 184, which is turned upside down from the state shown in FIG. 16A. The cover member 184 includes a fixed portion 52 having a through hole 50, and a cover portion 54 that covers a shaft receiving hole. The through hole 50 includes a stepped portion 56 that engages with the engaging stepped portion 42 of the sleeve 8. The structure of the stepped portion 56 is the same as that of the stepped portion 22 of each of the shaft receiving holes h1 and h2. The cover portion 54 includes a disc portion 58 that fits into the stepped portion 22 of each of the shaft receiving holes h1 and h2.

[0074] As shown in FIG. 15, the sleeve 8 is inserted through the through hole 50. The sleeve 8 is fixed to the shaft receiving hole h1, causing the fixed portion 52 to be sandwiched between the sleeve 8 and the shaft receiving hole h1. The fixed portion 52 is fixed to the hosel portion 16 by being sandwiched between the sleeve 8 and the shaft receiving hole h1. At this time, the engaging stepped portion 42 of the sleeve 8 engages with the stepped portion 56 of the fixed portion 52. Simultaneously, the shaft receiving hole h2, adjacent to the shaft receiving hole h1 to which the fixed portion 52 is fixed, is covered by the cover portion 54. The disc portion 58 of the cover portion 54 fits into the stepped portion 22 of the shaft receiving hole h2.

[0075] FIG. 17A and FIG. 17B show two different usage states of the cover member 184. As shown in FIG. 17A, when a shaft is inserted into the first shaft receiving hole h1, the fixed portion 52 is fixed to the first shaft receiving hole h1, and the cover portion 54 covers the second shaft receiving hole h2. As shown in FIG. 17B, when a shaft is inserted into the second shaft receiving hole h2, the fixed portion 52 is fixed to the second shaft receiving hole h2 and the cover portion 54 covers the first shaft receiving hole h1.

[0076] As described above, various specifications can be considered for the cover member 18. The cover member 18 may have a structure that is press-fitted into the shaft receiving hole h1 or h2, similar to a rubber stopper.

[0077] The above-described embodiments can exhibit the following advantageous effects.

[0078] When a head has a plurality of shaft receiving holes, and the shaft receiving holes are formed on different surfaces, or disposed independently and spaced apart from each other, it can cause a significant sense of incongruity for a golfer addressing a golf ball. This is because a shaft receiving hole (unused shaft receiving hole) without the shaft 6 inserted becomes conspicuous. However, in the above embodiments, the unused shaft receiving hole is located on the substantially flat upper end surface 16b, as with the other shaft receiving hole to which the shaft 6 inserted. As a result, the unused shaft receiving hole can be less conspicuous, which can reduce the sense of incongruity caused when addressing a golf ball.

[0079] By covering the unused shaft receiving hole with the cover member 18, the unused shaft receiving hole can become even less conspicuous. This can further reduce the sense of incongruity caused when addressing a golf ball.

[0080] The shaft receiving holes are located at different positions. This enables the adjustment of the specifications of the club by selecting one of the shaft receiving holes. For example, as shown in the embodiment of FIG. 5, when the face-back directional position (i.e., position in the face-back direction) of the first shaft receiving hole h1 differs from the face-back directional position of the second shaft receiving hole h2, the face progression of the head can be adjusted by selecting one of the shaft receiving holes. For example, as shown in the embodiment of FIG. 10, when the toe-heel directional position of the first shaft receiving hole h1 differs from the toe-heel directional position of the second shaft receiving hole h2, the distance of the center of gravity of the head can be adjusted by selecting one of the shaft receiving holes. The distance of the center of gravity of the head refers to the distance between the center of gravity of the head and the shaft axis line. Other specifications, such as the depth of the center of gravity of the head, lie angle, real loft angle, face angle, and moment of inertia of the head about the shaft axis line, can also be adjusted by selecting one of the shaft receiving holes. The plurality of shaft receiving holes can enhance the adjustability of the club specifications.

[0081] In the above embodiments, the first shaft receiving hole h1 is located on the face side relative to the second shaft receiving hole h2 (see FIG. 5, for example). When the position of the shaft receiving hole is changed in the face-back direction to adjust the face progression, ball catchability can be adjusted (ball catchability refers to the ability of a head to avoid an open striking face at impact with a golf ball). When the club has a small face progression, the ball catchability increases. Accordingly, a golfer who would like to reduce slice shots can reduce the face progression. Conversely, when the club has a greater face progression, the ball catchability reduces. Accordingly, a golfer who would like to reduce hook shots can increase the face progression.

[0082] A double-pointed arrow D1 in FIG. 5 indicates the distance between the center of the first shaft receiving hole h1 and the center of the second shaft receiving hole h2. The distance D1 is measured in the face-back direction. From the viewpoint of adjustability of the ball catchability, the distance D1 can preferably be greater than or equal to 15 mm, more preferably be greater than or equal to 16 mm, and still more preferably be greater than or equal to 17 mm. From the viewpoint of preventing the ball catchability from being excessively small when the second shaft receiving hole h2 is selected, the distance D1 can preferably be less than or equal to 25 mm, more preferably be less than or equal to 24 mm, and still more preferably be less than or equal to 23 mm.

[0083] In the first embodiment, the center line z2 of the second shaft receiving hole h2 is inclined toward the face side compared to the center line z1 of the first shaft receiving hole h1 (see FIG. 7). That is, the center line z2 of the shaft receiving hole h2 located on the back side is more inclined toward the face side (front side). As the shaft receiving hole is located at a further back side position, the face progression increases, causing the golfer to make an impact with a golf ball earlier in the downswing. When impact with a golf ball occurs earlier in the downswing, immediately before the impact where the orientation of the striking face gradually changes upward, the loft angle (real loft angle) of the head tends to be smaller at the impact with the ball. For this reason, the greater the face progression is, the smaller the dynamic loft angle of the head tends to be. When the shaft receiving hole h2 which has a greater face progression is inclined further toward the face side, the dynamic loft angle can increase, which can prevent a decrease in the launch angle of the struck ball. Note that the dynamic loft angle refers to a loft angle relative to the vertical direction.

[0084] When the real loft angle of the head 4 based on the center line z1 of the first shaft receiving hole h1 is referred to as a first real loft angle, and the real loft angle of the head 4 based on the center line z2 of the second shaft receiving hole h2 is referred to as a second real loft angle, then the second real loft angle is greater than the first real loft angle. A double-pointed arrow 2 in FIG. 7 indicates a difference between the second real loft angle and the first real loft angle (hereinafter, referred to as angle difference 2). Considering the compatibility between the angle difference 2 and the difference (distance D1) between face progressions, the lower limit of the angle difference 2 can be set to be greater than or equal to 0.5, further to be greater than or equal to 0.7, and still further to be greater than or equal to 1.0. From the same viewpoint, the upper limit of the angle difference 2 can be set to be less than or equal to 3.0, further to be less than or equal to 2.5, and still further to be less than or equal to 2.0.

[0085] In the first embodiment, the center line z2 of the second shaft receiving hole h2 is inclined toward the toe side compared to the center line z1 of the first shaft receiving hole h1 (see FIG. 2). That is, the center line z2 of the shaft receiving hole h2 located on the back side is more inclined toward the toe side. As the shaft receiving hole is located at a further back side position, the face progression increases, causing the golfer to make an impact with a golf ball earlier in the downswing. When impact with a golf ball occurs earlier in the downswing, immediately before the impact where the striking face gradually closes, the striking face tends to open at the impact with the ball. For this reason, the greater the face progression is, the more the striking face tends to open at impact with a golf ball. When the shaft receiving hole h2 is inclined further toward the toe side, the lie angle increases. In a golf club head having a loft angle of greater than 0, the higher the position of the toe side part compared to the position of the heel side part, the more closed the orientation of the face becomes. When the shaft receiving hole h2 is inclined further toward the toe side, the face can be oriented to close, which can suppress the deterioration of ball catchability.

[0086] When the lie angle of the head 4 based on the center line z1 of the first shaft receiving hole h1 is referred to as a first lie angle, and the lie angle of the head 4 based on the center line z2 of the second shaft receiving hole h2 is referred to as a second line angle, then the second lie angle is greater than the first lie angle. A double-pointed arrow 1 in FIG. 2 indicates a difference between the second lie angle and the first lie angle (hereinafter, referred to as angle difference 1). Considering the compatibility between the angle difference 1 and the difference (distance D1) between face progressions, the lower limit of the angle difference 1 can be set to be greater than or equal to 0.5, further to be greater than or equal to 0.7, and still further to be greater than or equal to 1.0. From the same viewpoint, the upper limit of the angle difference 1 can be set to be less than or equal to 3.0, further to be less than or equal to 2.7, and still further to be less than or equal to 2.0.

[0087] The entirety of the hosel portion 16 is located on the heel side relative to the face center Fc. The shaft receiving holes h1 and h2 can increase the weight of the hosel portion 16. The shaft receiving holes h1 and h2 place additional weight in the heel side part of the head 4. This reduces the distance of the center of gravity of the head and can improve the ball catchability. As a result, the head 4 can basically have an excellent ball catchability regardless of which shaft receiving hole is selected for insertion of the shaft. The distance of the center of gravity of the head refers to the distance between the shaft axis line and the center of gravity of the head.

[0088] In each of the above embodiments, each of the shaft receiving holes h1 and h2 includes the stepped portion 22. The stepped portion 22 engages with the sleeve 8, causing the sleeve 8 to be fixed to the hosel portion 16. When the center lines z1 and z2 of the shaft receiving holes h1 and h2 in a head have inclined angles different from each other, and when the upper end surface 16b engages with the sleeve 8, the orientation of the upper end surface 16b needs to vary for each of the shaft receiving holes h1 and h2. In this case, the upper end surface 16b cannot be a substantially flat surface. Conversely, in the above-described embodiments, the presence of each stepped portion 22 that engages with the sleeve 8 allows the orientation of the stepped portion 22 of the shaft receiving hole h1 to differ from the orientation of the stepped portion 22 of the shaft receiving hole h2, while enabling the upper end surface 16b to be a substantially flat surface. As described above, the presence of the stepped portions 22 of the shaft receiving holes h1 and h2 allows the inclination angles of the center lines z1 and z2 of the shaft receiving holes h1 and h2 to differ from each other while enabling the upper end surface 16b to be a substantially flat surface.

[0089] In the first embodiment, the head 4 includes the crown contour protruding portion 20 extending along the heel-side contour of the crown surface 12a. This holds true for the other embodiments as well. It is known that the phenomenon called toe down occurs due to the centrifugal force acting on the center of gravity of the head during a specific period of a golf swing, from the top of swing to the middle of the downswing. During this period, the head 4 moves with its heel-side portion preceding the remaining portion. However, the crown contour protruding portion 20 located in the heel-side portion of the head 4 increases the aerodynamic drag (force of air resistance) acting on the head 4. The increased aerodynamic drag cancels a part of the centrifugal force. Furthermore, during this period, the crown contour protruding portion 20 increases the lifting force acting on the head 4. That is, the crown contour protruding portion 20 increases the velocity of airflow on the upper side of the head 4, thereby increasing the lifting force, similar to the principle of lifting force acting on airplane wings. The increased aerodynamic drag and lifting force increase the force that cancels a part of the centrifugal force, which can suppress the toe down phenomenon.

[0090] The crown contour protruding portion 20 increases the weight of a part of the head 4 which is located on the contour of the head 4, which can increase a lateral MI of the head 4. The lateral MI refers to the moment of inertia of the head 4 about an axis that passes through the center of gravity of the head and extends in the up-down direction.

[0091] The crown contour protruding portion 20 can shift the position of the center of gravity of the head 4 toward the heel side. This facilitates face rotation during a swing, which can improve the ball catchability.

[0092] The crown contour protruding portion 20 extends from the protruding portion 16a. It appears that the crown contour protruding portion 20 is integrated with the protruding portion 16a (upper end surface 16b). The crown contour protruding portion 20, which extends continuously from the protruding portion 16a, can reduce the conspicuousness of the hosel portion 16. This can reduce the sense of incongruity caused when addressing a golf ball. The crown contour protruding portion 20 is continuous with the hosel portion 16a with no step. This can further reduce the conspicuousness of the hosel portion 16, and further reduce the sense of incongruity caused when addressing a golf ball.

[0093] In the embodiment shown in FIG. 10, the toe-heel directional position of the first shaft receiving hole h1 differs from the toe-heel directional position of the second shaft receiving hole h2. When the position of the shaft is changed in the toe-heel direction, the distance of the center of gravity of the head (distance between the shaft axis line Z and the center of gravity of the head) is changed. This change in the distance of the center of gravity of the head changes the moment of inertia of the head 24 about the shaft axis line. A smaller distance of the center of gravity of the head reduces the moment of inertia of the head 24 about the shaft axis line. This facilitates face rotation during a swing, which can improve the ball catchability.

[0094] In the embodiment shown in FIG. 11, the color of the hosel portion 16 is the same as the color of the crown contour protruding portion 20 when the crown surface 12a is viewed from the upper side. This enhances the unity in appearance between the hosel portion 16 and the crown contour protruding portion 20. Consequently, this can reduce the conspicuousness of the hosel portion 16, and can reduce the sense of incongruity caused when addressing a golf ball. Furthermore, in the embodiment shown in FIG. 11, the color of the hosel portion 16 and the crown contour protruding portion 20 differs from the color of the remaining area of the crown portion 12 when the crown portion 12 is viewed from the upper side. This design can create an optical illusion that the crown portion 12 consists only of a region where the hosel portion 16 and the crown contour protruding portion 20 is excluded from the crown portion 12, which can reduce the conspicuousness of the hosel portion 16. Consequently, this can reduce the sense of incongruity caused when addressing a golf ball.

[0095] The club length can also be adjusted by selecting one of the shaft receiving holes. For example, when the stepped portions 22 of the respective shaft receiving holes have depths that are different from each other, the club length can be adjusted by selecting one of the shaft receiving holes. However, various club lengths may be difficult for a single golfer to use. Additionally, the advantageous effects of adjustability brought by the shaft receiving holes can be diminished by the difference in club length. From this viewpoint, it is preferable that club length does not substantially change when the shaft receiving hole is changed. The difference in club length resulting from the variation in the shaft receiving holes can preferably be less than or equal to 0.5 inches (12.7 mm), more preferably less than or equal to 0.4 inches (10.2 mm), and still more preferably less than or equal to 0.3 inches (7.6 mm). The club length is measured in accordance with the rules prescribed by the Royal and Ancient Golf Club of Saint Andrews (R&A). These rules are described in 1c Length in 1 Clubs of Appendix II Design of Clubs of the latest version of Rules of Golf issued by the R&A. The measurement method is performed when the club is placed on a horizontal plane and the sole thereof is set against a plane having an angle of 60 degrees with respect to the horizontal plane. This method is therefore also referred to as the 60-degree measurement method.

[0096] Regarding the above-described embodiments, the following clauses are disclosed.

Clause 1

[0097] A golf club head including: [0098] a face portion including a striking face, [0099] a crown portion including a crown surface, [0100] a sole portion including a sole surface, and [0101] a hosel portion including a protruding portion that protrudes from the crown surface, wherein [0102] the hosel portion includes a single upper end surface that is a substantially flat surface, and a plurality of shaft receiving holes formed on the upper end surface, [0103] the shaft receiving holes include a first shaft receiving hole and a second shaft receiving hole, and [0104] the golf club head further includes a cover member that covers at least one of the shaft receiving holes which is not to have a shaft inserted.

Clause 2

[0105] The golf club head according to clause 1, wherein the first shaft receiving hole is located on a face side relative to the second shaft receiving hole.

Clause 3

[0106] The golf club head according to clause 1 or 2, wherein a center line of the second shaft receiving hole is inclined toward a face side compared to a center line of the first shaft receiving hole.

Clause 4

[0107] The golf club head according to any one of clauses 1 to 3, wherein a center line of the second shaft receiving hole is inclined toward a toe side compared to a center line of the first shaft receiving hole.

Clause 5

[0108] The golf club head according to any one of clauses 1 to 4, wherein [0109] the shaft receiving holes each have a stepped portion in a vicinity of the upper end surface, and [0110] the golf club head is configured such that a sleeve attached to a tip portion of a shaft is fixed to the hosel portion while engaging with the stepped portion of one of the shaft receiving holes.

Clause 6

[0111] The golf club head according to any one of clauses 1 to 5, wherein the upper end surface of the hosel portion extends along a heel-side contour of the crown surface.

Clause 7

[0112] The golf club head according to any one of clauses 1 to 6, wherein [0113] the golf club head further includes a crown contour protruding portion that extends along a heel-side contour of the crown surface from the upper end surface of the hosel portion toward a back side.

LIST OF REFERENCE SYMBOLS

[0114] 4, 24, 26 Head [0115] 6 Shaft [0116] 10 Face portion [0117] 10 a Striking face [0118] 12 Crown portion [0119] 12a Crown surface [0120] 14 Sole portion [0121] 14 a Sole surface [0122] 16 Hosel portion [0123] 16a Protruding portion [0124] 16b Upper end surface [0125] 18, 181, 182, 183, 184 Cover member [0126] 20 Crown contour protruding portion [0127] 22 Stepped portion [0128] 30 Screw [0129] h1 First shaft receiving hole [0130] h2 Second shaft receiving hole [0131] z1 Center line of the first shaft receiving hole [0132] z2 Center line of the second shaft receiving hole [0133] Z Shaft axis line

[0134] The above descriptions are merely illustrative and various modifications can be made without departing from the principles of the present disclosure.

[0135] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The use of the terms a, an, the, and similar referents in the context of throughout this disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used throughout this disclosure, the word may is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, as used throughout this disclosure, the terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted.