GOLF CLUB
20170274254 · 2017-09-28
Inventors
Cpc classification
A63B53/042
HUMAN NECESSITIES
A63B69/3617
HUMAN NECESSITIES
A63B53/0408
HUMAN NECESSITIES
A63B53/0416
HUMAN NECESSITIES
International classification
Abstract
A golf club includes a shaft, and a club head provided at an end of the shaft, wherein: the club head includes a head body and plate-like face member provided as a hitting face of the head body; and the face member is fixed to the head body only at a part of an upper or lower edge surface, or parts of both upper and lower edge surfaces of the face member. A fixing position of the face member may be located in the proximity of a node of a characteristic vibration in a case of freely supporting the face member. The Rockwell C-scale hardness of the face member is preferably no less than 40. The face member may be fixed to the head body by a set screw, at two locations of the upper edge surface, and two locations of the lower edge surface of the face member.
Claims
1. A golf club comprising a shaft, and a club head provided at an end of the shaft, wherein the club head comprises a head body, and a plate-like face member provided along a hitting face of the head body, and the face member is fixed to the head body only at a part of an upper edge surface, a part of a lower edge surface, or parts of both the upper and lower edge surfaces of the face member.
2. The golf club according to claim 1, wherein a fixing position of the face member is located in a proximity of a node of a characteristic vibration in a case of freely supporting the face member.
3. The golf club according to claim 1, wherein a Rockwell C-scale hardness of the face member is no less than 40.
4. The golf club according to claim 1, wherein the face member is fixed to the head body by a set screw.
5. The golf club according to claim 1, wherein the face member is fixed to the head body at two locations of the upper edge surface, and two locations of the lower edge surface of the face member.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0008]
[0009]
[0010]
[0011]
DESCRIPTION OF EMBODIMENTS
[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings as necessary.
[0013] The golf club of an embodiment of the present invention involves the features of: the club head including a head body and a plate-like face member provided as a hitting face of the head body; the face member being fixed to the head body only at a part of an upper edge surface, a part of a lower edge surface, or parts of both the upper and lower edge surfaces of the face member; and the upper edge surface and the lower edge surface being at least partially open. Therefore, since the face member has a relatively large area that can vibrate freely, the face member can vibrate relatively greatly. Accordingly, the golf club can generate a relatively large hitting sound, whereby a user can judge relatively easily whether a ball hit a sweet spot, based on the hitting sound.
[0014] It is preferred that a fixing position of the face member may be located in the proximity of a node of a characteristic vibration in a case of freely supporting the face member. Since the fixing position of the face member is thus located in the proximity of the node of the characteristic vibration in the case of freely supporting the face member, a fixed part of the face member is less likely to attenuate the vibration of the face member. Therefore, the present golf club can generate a hitting sound having a relatively long reverberation time period, whereby a user can judge more easily whether a ball hit a sweet spot, based on the hitting sound.
[0015] It is preferred that the Rockwell C-scale hardness of the face member is no less than 40. In the case of the Rockwell C-scale hardness of the face member being no less than the lower limit, the vibration of the face member is less likely to be attenuated relatively, leading to generation of a larger hitting sound and to a longer reverberation time period, whereby a user can judge more easily whether a ball hit a sweet spot, based on the hitting sound.
[0016] It is preferred that the face member may be fixed to the head body by a set screw. In the case of the face member being fixed to the head body by the set screw, the fixed part of the face member can be made small, and the attenuation of the hitting sound caused due to the vibration transmitted to the head body can be relatively reliably inhibited.
[0017] It is preferred that the face member is fixed to the head body at two locations of the upper edge surface, and two locations of the lower edge surface of the face member. In the case of the face member being fixed to the head body at two locations of the upper edge surface, and two locations of the lower edge surface of the face member, the face member can be fixed securely.
[0018] The term “freely supporting” as referred to herein means an ideal supporting state in which point of support is not fixed and vibrations are not inhibited. The “proximity” of a node of a characteristic vibration means that the distance from the node of the characteristic vibration in the heel-to-toe direction is no greater than one eight, and preferably no greater than one tenth the wavelength of the characteristic vibration. The “Rockwell C-scale hardness” as referred to means a value measured according to JIS-Z2245(2011).
First Embodiment
[0019] A golf club according to a first embodiment of the present invention illustrated in
Shaft
[0020] Publicly known shafts can be used for the shaft 1. A grip (not shown in the figure) held by a player (user) is attached to the end opposite to the club head 2 of the shaft 1.
[0021] Any shaft for a golf club can be used for the shaft 1. In other words, the material, diameter and length of the shaft 1 are not particularly limited.
Club Head
[0022] The club head 2 includes a head body 3 and a plate-like face member 4 provided along a hitting face of the head body 3. The face member 4 is fixed to the head body 3 at parts of the upper edge surface and parts of the lower edge surface, more specifically, only two locations of the upper edge surface and two locations of the lower edge surface.
[0023] The shape and size of the club head 2 are not particularly limited so long as it can be used as a golf club. More specifically, although a golf club is preferred which is manufactured according to the regulations set by an association such as Professional Golf Association (PGA), for example, it may not be manufactured necessarily according to such regulations, and thus, any golf club is acceptable so long as a user can hit a ball physically with it.
Head Body
[0024] The head body 3 includes a cavity 5 in which the face member 4 is provided on the front side (on the side of the ball in a hitting direction, i.e., on the side of a ball flying when hit). The cavity 5 is preferably formed in a rectangular shape which is longer in the heel-to-toe direction (a horizontal direction parallel to the hitting face) as viewed from the front which is perpendicular to the hitting face (observed from the front side in a forward/backward direction). In other words, it is preferred that the head body 3 is formed in a box-like shape opened at the front side. Furthermore, the head body 3 may be formed in a cylindrical shape or in a frame-like shape opened not only at the front side but also at the rear side.
[0025] The head body 3 includes a pair of screw holes 6 formed so as to extend through a top wall portion of the cavity 5 in a vertical direction, and a pair of fixing pins 7 provided to project in an upper direction so as to face the screw holes 6 at a bottom wall portion of the cavity 5. Set screws 8 (locking screws) are screwed into the screw holes 6, respectively.
[0026] The thickness of the head body 3 at regions of the top wall portion and the bottom wall portion of the cavity 5 into which the face member 4 is fit is set so as to have strength that can endure the impact to the head body 3 caused upon hitting of a ball with the golf club. More specifically, the lower limit of the average thickness of the head body 3 at the regions of the top wall portion and the bottom wall portion of the cavity 5 into which the face member 4 is fit is preferably 2 mm, and more preferably 3 mm. On the other hand, the upper limit of the average thickness of the head body 3 at the regions of the top wall portion and the bottom wall portion of the cavity 5 into which the face member 4 is fit is preferably 8 mm, and more preferably 6 mm. When the average thickness of the head body 3 at the regions of the top wall portion and the bottom wall portion of the cavity 5 into which the face member 4 is fit is less than the lower limit, the strength may be insufficient. To the contrary, when the average thickness of the head body 3 at the regions of the top wall portion and the bottom wall portion of the cavity 5 into which the face member 4 is fit is greater than the upper limit, the hitting face may be unnecessarily small. It should be noted that the thicknesses of the head body 3 at the top wall portion and at the bottom wall portion of the cavity 5 may differ from each other. According to the golf club of the present invention, in particular, when the thickness of the head body 3 at the bottom wall portion of the cavity 5 is greater than the upper limit, hitting a ball placed on the ground with the face member 4 at the center thereof in the vertical direction may be difficult.
[0027] The lower limit of the maximum length in the forward/backward direction of the head body 3 is preferably 2 cm, and more preferably 3 cm. On the other hand, the upper limit of the maximum length in the forward/backward direction of the head body 3 is preferably 15 cm, and more preferably 10 cm. When the maximum length in the forward/backward direction of the head body 3 is less than the lower limit, the strength of the head body 3 may be insufficient, or the fixation of the head body 3 to the shaft 1 may be difficult. To the contrary, when the maximum length in the forward/backward direction of the head body 3 is greater than the upper limit, handling of the golf club may be difficult.
[0028] Although a material of the head body 3 is not particularly limited, a metal such as stainless steel having a superior strength and processability is preferably used.
[0029] Furthermore, the lower limit of the effective diameter of the fixing pin 7 is preferably 1 mm, and more preferably 1.4 mm. On the other hand, the upper limit of the effective diameter of the fixing pin 7 is preferably 3 mm, and more preferably 2.5 mm. When the effective diameter of the fixing pin 7 is less than the lower limit, the strength may be insufficient so that the fixing pin 7 may be deformed or fractured when a user hits a ball. To the contrary, when the effective diameter of the fixing pin 7 is greater than the upper limit, the fixing pin 7 may inhibit the vibration of the face member 4. It should be noted that the “effective diameter” as referred to means a diameter of a part in contact with the face member 4.
[0030] Furthermore, the lower limit of the outer diameter (nominal diameter) of the set screw 8 is preferably 1.2 mm, and more preferably 1.8 mm. On the other hand, the upper limit of the outer diameter of the set screw 8 is preferably 4 mm, and more preferably 3 mm. When the outer diameter of the set screw 8 is less than the lower limit, the strength may be insufficient so that the set screw 8 may be deformed or fractured when a user hits a ball. To the contrary, when the outer diameter of the set screw 8 is greater than the upper limit, the set screw 8 may inhibit the vibration of the face member 4.
Face Member
[0031] The face member 4 is preferably formed in a rectangular shape which is longer in the heel-to-toe direction as viewed from the front. Furthermore, it is preferred that the face member 4 has a symmetrical shape in the heel-to-toe direction and the vertical direction, respectively. By forming the face member 4 symmetrically in the vertical and horizontal directions, the vibration of the face member 4 results in a standing wave and the vibration of a specific wavelength becomes large so that a relatively large sound can be generated.
[0032] This face member 4 is retained substantially vertically with respect to the hitting direction by the fixing pin 7 and the set screws 8 so as to substantially seal an opening portion of the cavity 5 and form gaps between each of peripheral walls (a top wall, a bottom wall, and a side wall) of the cavity 5 and a rear wall of the cavity 5, respectively. It is preferred that the face member 4 is provided such that a surface on the front side thereof is situated on the same plane as a front end face of the peripheral wall of the head body 3, or situated forward from the front end face thereof.
[0033] The lower limit of the average width in the vertical direction of the face member 4 is preferably 8 mm, and more preferably 10 mm. On the other hand, the upper limit of the average width in the vertical direction of the face member 4 is preferably 40 mm, and more preferably 20 mm. When the average width in the vertical direction of the face member 4 is less than the lower limit, hitting a ball on the face member 4 may not be easy. To the contrary, when the average width in the vertical direction of the face member 4 is greater than the upper limit, hitting the ball at the center in the vertical direction of the face member 4 may be difficult.
[0034] The lower limit of the average width in the heel-to-toe direction of the face member 4 is preferably 4 cm, and more preferably 5 cm. On the other hand, the upper limit of the average width in the heel-to-toe direction of the face member 4 is preferably 8 cm, and more preferably 7 cm. When the average width in the heel-to-toe direction of the face member 4 is less than the lower limit, the sweet spot on the face member 4 may be small. To the contrary, when the average width in the heel-to-toe direction of the face member 4 is greater than the upper limit, the width in the heel-to-toe direction of the club head may be too large.
[0035] The lower limit of the average space between the face member 4 and the peripheral wall of the cavity 5 is preferably 0.5 mm, and more preferably 1 mm. On the other hand, the upper limit of the average space between the face member 4 and the peripheral wall of the cavity 5 is preferably 5 mm, and more preferably 3 mm. When the average space between the face member 4 and the peripheral wall of the cavity 5 is less than the lower limit, air vibrations at the backside of the face member 4 are less likely to be transmitted to the outside, and thus, a hitting sound may be small or a reverberation may be shortened. To the contrary, when the average space between the face member 4 and the peripheral wall of the cavity 5 is greater than the upper limit, the hitting face may be unnecessarily small.
[0036] The lower limit of the average space in the forward/backward direction between the face member 4 and the rear wall of the cavity 5 is preferably 3 mm, and more preferably 5 mm. On the other hand, the upper limit of the average space between the face member 4 and the rear wall of the cavity 5 is preferably 5 cm, and more preferably 3 cm. When the average space between the face member 4 and the rear wall of the cavity 5 is less than the lower limit, an air space between the face member 4 and the rear wall of the cavity 5 may inhibit the vibration of the face member 4. To the contrary, when the average space between the face member 4 and the rear wall of the cavity 5 is greater than the upper limit, the club head 2 may be too large.
[0037] In order to securely fix the face member 4 to the head body 3, the face member 4 may include a pair of upper counterbores 9 which is formed at the upper edge surface of the face member 4 and with which the set screws 8 are engaged, and a pair of lower counterbores 10 which is formed at the lower edge surface of the face member 4 and with which the fixing pins 7 are engaged.
[0038] In addition, it is preferred that one of the upper counterbore 9 and the lower counterbore 10 has a recess portion in a rotary-surface shape at which a cross-sectional area in a conical shape, in a spherical shape, etc., decreases monotonously, and the other one of the upper counterbore 9 and the lower counterbore 10 has a groove shape in which a width in a V-groove shape, etc., decreases monotonously. When one of the upper counterbore 9 and the lower counterbore 10 is thus formed in a groove shape, a dimensional error in the heel-to-toe direction along the head body 3 and the hitting face of the face member 4 can be absorbed.
[0039] The lower limit of the average width of the upper counterbore 9 and the lower counterbore 10 is preferably 1 mm, and more preferably 1.5 mm. On the other hand, the upper limit of the average width of the upper counterbore 9 and the lower counterbore 10 is preferably 5 mm, and more preferably 3 mm. When the average width of the upper counterbore 9 and the lower counterbore 10 is less than the lower limit, the engagement with the set screw 8 or the fixing pin 7 may be insufficient. To the contrary, when the average width of the upper counterbore 9 and the lower counterbore 10 is greater than the upper limit, the face member 4 may not be positioned precisely, or the vibration of the face member 4 may be disturbed.
[0040] The lower limit of the maximum depth of the upper counterbore 9 and the lower counterbore 10 is preferably 0.3 mm, and more preferably 0.5 mm. On the other hand, the upper limit of the maximum depth of the upper counterbore 9 and the lower counterbore 10 is preferably 1.5 mm, and more preferably 1 mm. When the maximum depth of the upper counterbore 9 and the lower counterbore 10 is less than the lower limit, the engagement with the set screw 8 or the fixing pin 7 may be insufficient. To the contrary, when the maximum depth of the upper counterbore 9 and the lower counterbore 10 is greater than the upper limit, the vibration of the face member 4 may be disturbed.
[0041] It is preferred that positions of the upper counterbore 9 and the lower counterbore 10 in the heel-to-toe direction, i.e., fixing positions of the face member 4 are located in the proximity of a node of a characteristic vibration in the case of freely supporting the face member 4. By supporting in the proximity of the node of the characteristic vibration in the case of freely supporting the face member 4, the structure of fixing the face member 4 does not inhibit the vibration of the face member 4. In other words, by providing the set screw 8 and the fixing pin 7 at the node of the characteristic vibration, vibration energy to the head body 3 through the set screw 8 and the fixing pin 7 does not diffuse. Therefore, the attenuation of the vibration of the face member 4 can be inhibited. Accordingly, since the face member 4 of the embodiment of the present invention results in a longer reverberation which is generated when a player hits a ball with the golf club, the player can discriminate the hitting sound easily.
[0042] Furthermore, by supporting in the proximity of the node of the characteristic vibration in the case of freely supporting the face member 4, the center of the face member 4, as viewed from the front, corresponds to an antinode of the vibration. The location corresponding to the antinode of the vibration of the face member 4 is a sweet spot in which the repulsive force due to the elasticity of the face member 4 can be easily attained, thereby enabling kinetic energy of the club head 2 to be transmitted to the ball precisely. Moreover, the location corresponding to the antinode of the vibration is also a location at which the face member 4 can be most efficiently vibrated.
[0043] Thus, upon hitting of the ball at the sweet spot when the ball is hit with the golf club, the face member 4 vibrates with a larger amplitude so that a larger sound having a longer reverberation is generated. Furthermore, as the ball hitting location deviates from the sweet spot, a vibration having a frequency component different from a resonance frequency of the characteristic vibration is likely to be generated first. Therefore, according to the golf club, whether the ball hit the sweet spot can be determined relatively easily based on a tone of the hitting sound, sound pressure, and the length of a reverberation.
[0044] It is preferred that a characteristic vibration in which the fixing position of the face member 4 is located at a node is an odd-order vibration mode. In a case in which the face member 4 is homogeneous and in a rectangular plate shape having a constant thickness, the center portion of the face member 4 in the heel-to-toe direction corresponds to an antinode of the vibration, i.e. the sweet spot, in the odd-order vibration mode, and therefore the golf club having such a configuration can be used conveniently.
[0045] It is particularly preferred that the characteristic vibration in which the fixing position of the face member 4 is located at the node is the primary vibration mode. Among the vibration modes in each order, the primary vibration mode has the largest interval of nodes and allows the largest amplitude to be attained with respect to hitting energy. Therefore, by fixing the face member 4 to the head body 3 at the node in the primary vibration mode, the sweet spot can be made larger, thereby enabling a larger hitting sound to be generated. More specifically, in a case in which the face member 4 is homogeneous and in a rectangular plate shape having a constant thickness, the node of the characteristic vibration is approximately 0.224 times the length of the face member 4, from each of the both ends thereof.
[0046] The lower limit of the average thickness between the fixing positions of the face member 4 (the region along the line between the opposed upper counterbore 9 and counterbore 10) is preferably 1 mm, and more preferably 1.5 mm. On the other hand, the upper limit of the average thickness between the fixing positions of the face member 4 is preferably 10 mm, and more preferably 8 mm. When the average thickness between the fixing positions of the face member 4 is less than the lower limit, the strength of the face member 4 may be insufficient. To the contrary, when the average thickness between the fixing positions of the face member 4 is greater than the upper limit, a characteristic vibration frequency of the face member 4 (i.e. frequency of a hitting sound) may be smaller, and thus hearing the hitting sound may be difficult.
[0047] The thickness of the face member 4 may be totally constant or may vary in part. For example, in a case in which the thickness in the proximity of the both ends of the face member 4 in the heel-to-toe direction is made greater than the thickness at the center portion in the heel-to-toe direction, the mass of the both ends thereof in the heel-to-toe direction is greater and a node of the characteristic vibration of the face member 4 becomes closer to the both ends thereof in the heel-to-toe direction than the case of the thickness of the face member 4 being constant. Accordingly, the range in which the amplitude of the characteristic vibration is great can be expanded, whereby the sweet spot of the golf club can be made larger.
[0048] The node of the characteristic vibration of the face member 4 can be moved by attaching a weight in the proximity of the both ends of the face member 4 in the heel-to-toe direction. In addition, it is preferred that the thickness (weight) of the face member 4 does not vary in the vertical direction. If the thickness of the face member 4 varies in the vertical direction, a component of the characteristic vibration in the vertical direction may be generated so that a progressive wave is formed and thus the sound may be distorted or the sound pressure may be reduced.
[0049] A material of the face member 4 is preferably steel having a relatively greater hardness, and more preferably steel subjected to a quenching treatment. By forming the face member 4 with a material having such a greater hardness, the characteristic vibration frequency of the face member 4 can be made relatively higher, and thus hearing of the hitting sound can be facilitated. It should also be noted that the surface of the face member 4 may be subjected to an anti-corrosive treatment such as solid chrome plating.
[0050] The lower limit of the a Rockwell C-scale hardness (HRC) of the face member 4 is preferably 40, more preferably 50, and further preferably 55. On the other hand, the upper limit of the Rockwell C-scale hardness of the face member 4 is preferably 80, and more preferably 75. When the Rockwell C-scale hardness of the face member 4 is less than the lower limit, the characteristic vibration frequency of the face member 4 (i.e. the frequency of the hitting sound) may be small and the vibration may be easily attenuated, so that it may be difficult for a user to hear the hitting sound. To the contrary, when the Rockwell C-scale hardness of the face member 4 is greater than the upper limit, processing of the face member 4 may be difficult, and thus the golf club may be unnecessarily expensive.
Advantages
[0051] As described above, according to the golf club of the embodiment of the present invention, since the face member 4 is fixed to the head body 3 only at the parts (four locations) of the upper and lower edge surfaces thereof, the face member 4 easily vibrates and thus a relatively large hitting sound with a long reverberation is generated. Furthermore, upon hitting of a ball at an antinode of the characteristic vibration corresponding to the sweet spot of the face member 4, the hitting sound has a smaller distortion and larger sound pressure. Therefore, according to the golf club of the embodiment of present invention, whether the ball hit the sweet spot can be judged relatively easily based on the hitting sound.
Second Embodiment
[0052] A golf club according to another embodiment of the present invention illustrated in
[0053] The shaft 1 of the golf club shown in
Club Head
[0054] The club head 2a includes a head body 3a and a plate-like face member 4a provided along a hitting face of the head body 3a. The face member 4a is fixed to the head body 3a only at two locations on an upper edge surface of the face member 4a. In other words, a lower edge surface of the face member 4a is not fixed to the head body 3a.
[0055] The configuration of the head body 3a and the face member 4a of the golf club shown in
[0056] Two fixation projections 11 are provided at the face member 4a so as to project upward, respectively, from the locations of two nodes of the characteristic vibration on the upper edge surface of the face member 4a. The fixation projections 11 may be carved out integrally with the face member 4a from a plate-like material, for example. Alternatively, the fixation projections 11 may be fixed to the face member 4a by welding, etc.
[0057] The face member 4a is fixed so as to substantially seal an opening of a cavity 5 by attaching the fixation projections 11 at a front end face of a top wall of the cavity 5 of the head body 3a. The fixation projections 11 are preferably fit into fitting recess portions formed on the front end face of the top wall of the head body 3a.
[0058] For a fixing procedure of the fixation projections 11 to the head body 3, although welding, etc., may be used, for example, a procedure in which screws 12 are used may be preferably employed, as illustrated in
[0059] Furthermore, the widths of portions extending from the upper edge surface in the heel-to-toe direction of the fixation projections 11 may be made shorter, as illustrated in the figure, so that the vibration of the face member 4 is less likely to be restricted.
Other Embodiments
[0060] The above-described embodiments do not limit the configurations of the present invention. Therefore, omissions, replacements, and/or additions of constituent elements of each component in the above-described embodiments can be made based on the disclosure of the specification of the present application and technical common knowledge, and thus, all such modifications thereof shall be construed as being within the scope of the present invention.
[0061] The present invention may be applied also to golf clubs other than putters, such as woods (for example, drivers) and irons (for example, approach wedges).
[0062] The shape of the face member as viewed from the front according to the golf club of the other embodiment of the present invention is not limited to the rectangular shape and may be in any shape, such as an oblong shape, a semi-elliptical shape, and a triangle shape. However, when considering the diameter of a ball, the face member is preferably in a shape in which a lower edge of the face member extends linearly in the heel-to-toe direction or is in a slightly downwardly convex shape so that a user can hit the ball at the center of the face member, without the club head being brought into contact with the ground.
[0063] A fixation method for the face member in the golf club of the other embodiment of the present invention is not limited to the methods according to the above-described embodiments, and any method can be adopted.
[0064] For example, the face member may be fixed to the head body by using a pin which penetrates from the head body to the upper edge surface of the face member. Furthermore, when using a set screw, the lower side of the face member may be fixed by the set screw, or both the upper and lower sides may be fixed by the set screw.
[0065] Still further, also when providing the fixation projections to the face member, the fixation projections may be provided at the upper portion and the lower portion so as to fix the both upper and lower edges. In such a case, the fixation projection at the lower side may be simply fit into a fitting recess portion of the head body without being screwed. According to such a configuration, a bottom wall of the head body can be easily made thinner.
[0066] Furthermore, the face member in the golf club of the embodiment of the present invention may be fixed to the head body only at a single location of the upper edge surface, a single location of the lower edge surface, or each single location at the upper and lower edge surfaces. Moreover, a fixed location at the upper edge surface in the horizontal direction may differ from a fixed location at the lower edge surface in the horizontal direction. For an example, an upper end of one of two resonance points of the face member and a lower end of the other one of the two resonance points of the face member may be fixed, whereas a lower end of the one resonance point and an upper end of the other resonance point may not be fixed.
[0067] In addition, according to the golf club of the embodiments of the present invention, the head body may include a through-hole through which a sound can be passed, at the peripheral wall or the rear wall of the cavity.
INDUSTRIAL APPLICABILITY
[0068] The golf club according to the present invention can be preferably used as a putter, in particular.
EXPLANATIONS FOR REFERENCE NUMERALS
[0069] 1 shaft [0070] 2,2a club head [0071] 3,3a head body [0072] 4,4a face member [0073] 5 cavity [0074] 6 screw hole [0075] 7 fixing pin [0076] 8 set screw [0077] 9 upper counterbore [0078] 10 lower counterbore [0079] 11 fixation projection [0080] 12 screw [0081] 13 fixation hole