SECURITY FASTENERS

Abstract

A security fastener for use with a corresponding driver, the fastener comprising: a shank defining a longitudinal centre axis; and a head having a face for mating with a corresponding security bit of the driver, the face including at least one recess for receiving a corresponding projection of the bit, wherein the head has: 1-fold rotational symmetry about the longitudinal centre axis of the shank; and a maximum of 1 mirror plane containing the longitudinal centre axis, such that mating of the corresponding projection of the driver with any of the at least one recesses is achievable only when the driver is in a single angular position with respect to the head, wherein the face comprises a first surface and the at least one recess is defined within the first surface, further wherein the longitudinal centre axis intersects the first surface.

Claims

1. A security fastener for use with a corresponding driver, the fastener comprising: a shank defining a longitudinal centre axis; and a head having a face for mating with a corresponding security bit of the driver, the face including at least one recess for receiving a corresponding projection of the bit, wherein the head has: 1-fold rotational symmetry about the longitudinal centre axis of the shank; and a maximum of 1 mirror plane containing the longitudinal centre axis, such that mating of the corresponding projection of the driver with any of the at least one recesses is achievable only when the driver is in a single angular position with respect to the head, wherein the face comprises a first surface and the at least one recess is defined within the first surface, further wherein the longitudinal centre axis intersects the first surface, wherein the head has a periphery and wherein each of the at least one recesses is open at the periphery of the head.

2. A security fastener according to claim 1, wherein the face has a first side and an opposing second side, wherein each of the at least one recesses extends only on one of the first and second sides.

3. A security fastener according to claim 1, wherein the face comprises a first surface and the at least one recess is defined within the first surface, wherein a transition between the first surface and each of the at least one recesses forms a respective engagement surface, each engagement surface being parallel to the longitudinal centre axis.

4. A security fastener according to claim 3, wherein each of the engagement surfaces are described entirely by one of a single straight line or a single arc of constant radius when viewed along the longitudinal centre axis.

5. A security fastener according to claim 4, wherein each one of the engagement surfaces which is described by a straight line when viewed along the longitudinal centre axis is angled with respect to every other one of the engagement surfaces which is described by a straight line when viewed along the longitudinal axis.

6. A security fastener according to claim 3, wherein the at least one recess comprises a first recess and a second recess, wherein: a transition between the first surface and the first recess is formed by a first engagement surface, said first engagement surface being described entirely by a straight line when viewed along the longitudinal centre axis; and a transition between the first surface and the second recess is formed by a second engagement surface, said second engagement surface being described entirely by a single arc of constant radius when viewed along the longitudinal centre axis.

7. A security fastener according to claim 6, wherein the first recess and the second recess are arranged diametrically opposite one another on the head.

8. A security fastener according to claim 6, wherein the at least one recess comprises a third recess, wherein a transition between the first surface and the third recess is formed by a third engagement surface, said third engagement surface being described entirely by a single straight line when viewed along the longitudinal centre axis.

9. A security fastener according to claim 8, wherein the face has a single mirror plane containing the longitudinal centre axis.

10. A security fastener according to claim 8, wherein the third recess is substantially a mirror image of the first recess, the mirror plane containing the longitudinal centre axis.

11. A security fastener according to claim 1, wherein at least a portion of the shank is threaded.

12. A driver for a security fastener according to any of claims 1 to 11, the driver including a security bit for mating with the face of the fastener, the bit comprising, for each one of the at least one recesses, a respective corresponding projection configured to mate with the respective one of the at least recesses, said projections comprising a driving surface configured to engage an engagement surface of the respective recess and thereby transfer torque to the fastener to rotate the fastener.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0012] The invention will now be described, by way of example, with reference to the following figures, in which:

[0013] FIG. 1 is a side view of a first embodiment of a security fastener according to the present invention;

[0014] FIG. 2 is a plan view of the security fastener of FIG. 1;

[0015] FIG. 3 is an isometric view of a driver for installing and removing the fastener of FIG. 1;

[0016] FIG. 4 is an enlarged side view of the security bit of the driver of FIG. 3;

[0017] FIG. 5 is a plan view of the security bit of FIG. 4;

[0018] FIG. 6 is a side view of a second embodiment of a security fastener according to the present invention;

[0019] FIG. 7 is a plan view of the security fastener FIG. 6;

[0020] FIG. 8 is an enlarged side view of the security bit of the driver of FIG. 6;

[0021] FIG. 9 is a plan view of the security bit of FIG. 8;

[0022] FIGS. 10 to 12 show a method of manufacturing a security fastener according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE FIGURES

[0023] Referring to FIGS. 1 and 2, a fastener 10 according to a first embodiment of the present invention comprises a head 12 and a shank 14. The shank 14 defines a longitudinal centre axis 16 and preferably comprises a threaded portion 18 which may extend along the full length of the shank 14. Alternatively, as illustrated in FIGS. 1 and 2, the shank 14 may include a threaded portion 18 and a non-threaded portion 20. The head 12 is generally cylindrical and has a face designed to be engaged by a corresponding security bit of a driver according to the invention. When viewed along the longitudinal centre axis 16, the face defines a circular periphery 22. The face includes a first surface 24 and first and second recesses 26,28 defined within the first surface 24. Each of the first and second recesses 26,28 is open at the periphery 22 of the head.

[0024] Each of the first and second recesses 26,28 is defined by an indented, or recessed, surface within the first surface 24. The transition between the indented surface of the first recess 26 and the first surface 24 comprises a wall defining a first engagement surface 30 that extends parallel to the longitudinal centre axis 16. The transition between the indented surface of the second recess 28 and the first surface 24 comprises a wall defining a second engagement surface 32 that extends parallel to the longitudinal centre axis 16.

[0025] It will of course be appreciated that whilst the particular embodiment shown in FIGS. 1 and 2 is provided with two recesses, other embodiments may include only a single recess or include more than two recesses.

[0026] In the embodiment shown in FIGS. 1 and 2, when viewed along the longitudinal centre axis 16, the first engagement surface 30 between the first surface 24 and the first recess 26 describes an arc which intersects the circular periphery of the face of the head 12 at first and second points on the periphery 22, such that the first recess 26 comprises a lens shape. The arc described by the first engagement surface 30 preferably has a smaller radius than the radius of the circular periphery of the face, such that the first recess 26 has as an asymmetric lens shape.

[0027] The second engagement surface 32 is substantially flat, or planar. As such, when viewed along the longitudinal centre axis 16, the second engagement surface 32 describes a chord of the face, such that the second recess 28 has a segment shape.

[0028] The first 24 and second 26 recesses are disposed diametrically opposite each other on the face. As such, a mirror plane is defined along the diameter of the face through a centre line of the lens and segment defined respectively by the first 24 and second recesses 26.

[0029] Referring to FIGS. 3 to 5, a driver 34 for installing and removing the fastener 10 according to the first embodiment comprises a handle 36 and a security bit 38 configured to mate with the face of the fastener 10, as will be described in more detail below. The security bit 38 defines a longitudinal centre axis 40 and includes first and second projections 42,44 which extend along a direction parallel to the longitudinal centre axis 40, and which correspond respectively to the first 26 and second 28 recesses of the fastener 10.

[0030] Referring in particular to FIG. 4, the first projection 42 has a form which is complementary to the first recess 26 of the fastener 10, and comprises a first driving surface 46 which extends parallel to the longitudinal centre axis 40 of the driver, and a first distal surface 48 which extends perpendicular to said longitudinal centre axis 40. The first distal surface 48 comprises an asymmetric lens shape which is congruent with the asymmetric lens shape of the first recess 26.

[0031] The second projection 44 has a form which is complementary to the second recess 28 of the fastener 10, and comprises a second driving surface 54 which extends parallel to the longitudinal centre axis 40 of the driver, and a second distal surface 56 which extends perpendicular to said longitudinal centre axis 40. The second distal surface 56 comprises a segment shape which is congruent with the segment shape of the second recess 28.

[0032] In use, the fastener 10 of the second embodiment is installed or removed in a hole or bore in an object by rotating the fastener 10 using the driver 34. The bit 38 of the driver 34 is mated with the face of the head 12 by engaging the first and second projections 42,44 in the first and second recesses 26,28, respectively. In this configuration, the first driving surface 52 of the first projection 42 is engaged with the first engagement surface 30 of the first recess 26, the second driving surface 54 of the second projection 44 is engaged with the second engagement surface 32 of the second recess 28. An operator then rotates the driver 34 in the appropriate direction using the handle 36. Torque is transferred to the fastener 10 through the driving surfaces 52,54 to the engagement surfaces 30,32 causing the fastener 10 to rotate to either insert or remove the fastener, as desired.

[0033] It will be understood that the angularly spaced arrangement of the recesses around the periphery of the head means that to apply sufficient torque to the fastener 10 to rotate the fastener, torque must be applied to each of the first and second engagement surfaces 30,32. As such, only a tool having a shape capable of mating with both recesses 62,64,66 will be able to remove the fastener 10. Due to the low degree of symmetry of the recesses on the face (the face has 1-fold mirror symmetry, and 1-fold rotational symmetry only), standard tools are unable to engage both recesses 26,28 simultaneously. Thus, removal of the fastener is restricted to those in possession of the driver 34.

[0034] It will also be appreciated that the use of an arcuate engagement surface, as in the first recess 26, in opposing relationship with the planar engagement surface of the second recess 28 means that the head presents no parallel opposing engagement surfaces. This makes it difficult to apply sufficient force to the engagement surfaces to rotate the fastener 10 by gripping the engagement surfaces using a gripping tool such as a wrench.

[0035] Referring to FIGS. 6 and 7, a fastener 10 according to a second embodiment of the present invention will now be described. The second embodiment has many elements in common with the first embodiment and like reference numerals are used for like elements. In the following description, only differences between the first and second embodiments will be described in detail.

[0036] The second embodiment of the fastener 10 comprises a head 12 having a face which includes a first surface 24 and first, second and third recesses 62,64,66. The transition between the indented surface of the first recess 62 and the first surface 24 comprises a wall defining a first engagement surface 68 that extends parallel to the longitudinal centre axis 16 of the fastener 10. The transition between the indented surface of the second recess 64 and the first surface 24 comprises a wall defining a second engagement surface 70 that extends parallel to the longitudinal centre axis 16. The transition between the indented surface of the third recess 66 and the first surface 24 comprises a wall defining a third engagement surface 72 that extends parallel to the longitudinal centre axis 16.

[0037] The first engagement surface 68 between the first surface 24 and the first recess 62 is substantially flat, or planar. As such, when viewed along the longitudinal centre axis 16, the first engagement surface 68 describes a chord of the face, such that the first recess 62 has a segment shape.

[0038] The second engagement surface 70 describes an arc which intersects the circular periphery 22 of the face of the head 12 at first and second points on said periphery, such that the second recess 64 comprises a lens shape. The arc described by the second engagement surface 70 has a smaller radius than the radius of the circular periphery 22 of the face, such that the second recess 64 has as an asymmetric lens shape.

[0039] The third engagement surface 72 between the first surface 24 and the third recess 66 is substantially flat, or planar. As such, when viewed along the longitudinal centre axis 16, the third engagement surface 72 describes a chord of the face, such that the third recess 66 has a segment shape. The chord described by the third engagement surface 70 has a length which is substantially the same as the length of the chord described by the first engagement surface 68.

[0040] The face of the second embodiment of the fastener 10 has a mirror plane M (shown by a dashed line in FIG. 7) which contains the longitudinal centre axis 16 and which divides the face into a first side 55 and an opposing second side 57. Each of the first and second sides 55,57 define equal semi-circular portions of the face. The first recess 62 is arranged on the first side 55 of the face and the third recess 66 is arranged on the second side 57 of the face. The third recess 66 comprises a mirror image of the first recess 62 through the mirror plane M. The second recess 64 is arranged between the first and second sides of the face and is centred on the mirror plane M. The first engagement surface 68 of the first recess 72 is angled with respect to the mirror plane M. In particular, the first engagement surface 68 is angled away from the mirror plane M in a direction towards the second recess 64. Since the third recess 66 is a mirror image of the first recess 62, the third recess 66 is also necessarily angled away from the mirror plane M in a direction towards the second recess 64.

[0041] Referring to FIGS. 6 and 7, a driver 34 for installing and removing the fastener 10 according to the second embodiment comprises a security bit 38 including first, second and third projections 76,78,80 which each project along a direction parallel to the longitudinal centre axis 40 of the bit 38. The first, second and third projections 76,78,80 correspond respectively to the first, second and third recesses 62,64,66 of the fastener 10 and are disposed in spaced angular relationship around the longitudinal centre axis 40 of the bit 38.

[0042] The first projection 76 has a form which is complementary to that of the first recess 62 of the fastener 10, and comprises a first driving surface 82 which extends parallel to the longitudinal centre axis 40 of the driver, and a first distal surface 84 which extends perpendicular to said longitudinal centre axis 40. The first distal surface 84 comprises a segment shape which is congruent with the segment shape of the first recess 62.

[0043] The third projection 80 has a form which is complementary to that of the third recess 66 of the fastener 10, and comprises a third driving surface 98 which extends parallel to the longitudinal centre axis 40 of the driver, and a third distal surface 100 which extends perpendicular to said longitudinal centre axis 40. The third distal surface 100 comprises a segment shape which is congruent with the segment shape of the third recess 66. The third projection 80 is a mirror image of the first projection 76 through a mirror plane containing the longitudinal centre axis 40.

[0044] The second projection 78 has a form which is complementary to that of the second recess 64 of the fastener 10 and comprises a second driving surface 90 which extends parallel to the longitudinal centre axis 40 of the driver, and a second distal surface 92 which extends perpendicular to said longitudinal centre axis 40. The second distal surface 92 comprises an asymmetric lens shape which is congruent with the asymmetric lens shape of the second recess 64.

[0045] In use, the fastener 10 of the second embodiment is installed in a hole or bore in an object by rotating the fastener 10 using the driver 34 of the second embodiment. The bit 38 of the driver 34 is mated with the face of the head 12 by engaging the first, second and third projections 76,78,80 in the first, second and third recesses 62,64,66, respectively. In this configuration, the first driving surface of the first projection is engaged with the first engagement surface 68 of the first recess 62, the second driving surface 70 of the second projection is engaged with the second engagement surface of the second recess, and the third driving surface 72 of the third projection 66 is engaged with the third engagement surface of the third recess. An operator then rotates the driver 34 using the handle 36. Torque is transferred to the fastener 10 through the driving surfaces 82,90,98 to the engagement surfaces 68,70,72 causing the fastener 10 to rotate. As the fastener 10 rotates the right-handed thread pulls the fastener 10 into the hole/bore. The driver 34 is then rotated until the fastener 10 bears against the surface of the object.

[0046] To remove the fastener 10, the bit 38 is again mated with the driver 34 by engaging the first, second and third projections 76,78,80 in the first, second and third recesses 62,64,66, respectively and the driver 34 rotated in the opposite direction.

[0047] It will be understood that the angularly spaced arrangement of the recesses around the periphery of the head means that in order to apply sufficient torque to the fastener 10 to rotate the same, torque must be applied to each of the first second and third engagement surfaces 68,70,72. As such, only a tool having a shape capable of mating with all three recesses 62,64,66 will be able to remove the fastener 10. Due to the low symmetry of the recesses on the face (the face has 1-fold mirror symmetry, and 1-fold rotational symmetry only), standard tools are unable to engage each of the recesses 62,64,66. Thus removal of the fastener is restricted to those in possession of the driver 34 of the second embodiment.

[0048] Like the first embodiment, the second embodiment also presents no parallel opposing engagement surfaces, making it difficult to apply sufficient force to the engagement surfaces to rotate the fastener 10 by gripping the engagement surfaces 68,70,72 using a gripping tool such as a wrench.

[0049] A method of manufacturing a security fastener as illustrated in the previous figures will now be described with reference to FIGS. 10 to 12.

[0050] Referring in particular to FIG. 10, a first step of the method comprises providing a preform 10 of the fastener. The preform 10 comprises a shank 14 defining a longitudinal centre axis 16 and a head 12 having a first surface facing along the longitudinal centre axis 16. The first surface 24 has a circular periphery 22 and a first side 50 and an opposing second side 52.

[0051] Still referring to FIG. 10, a second step of the method comprises cutting a first recess 26 into the first side 50 of the first surface of the head 12. Preferably, the recesses are cut into the first surface by milling the head 12 using a rotary cutter 102.

[0052] To cut the first recess 26 into head 12, the rotary cutter 102 is translated in a first radial direction D1 to move the cutter 102 partially into the head 12 through the periphery of the head 12. The cylindrical cutter is then moved out of the head again by translating the cylindrical cutter in a reverse radial direction through the periphery. This results in an asymmetric lens-shaped recess which is open at the periphery 22 of the head, as shown in FIG. 11.

[0053] The transition between the indented surface of the first recess 26 and the first surface 24 comprises a first engagement surface 30 that extends parallel to the longitudinal centre axis. When viewed along the longitudinal centre axis 16, the first engagement surface 30 is described by an arc having a radius equal to the radius of the cylindrical cutter.

[0054] A subsequent step in the method comprises cutting a second recess 28 into the second side 52 of the first surface 24 of the head 12. To cut the second recess 28 into the head, the cylindrical cutter is translated in a lateral direction D2 to move the cutter into the second side of the head 12 through the periphery 22 of the head 12. The cutter is then advanced in a straight line along the lateral direction D2 through the head 12 and thereafter exits the head 12 through the periphery 22 of the first surface 24. This results in a segment shaped recess which is open at the periphery of the head 12, as shown in FIG. 12.

[0055] In some embodiments, the recesses are cut whilst the preform is maintained substantially at room temperature. Such cold-forging processes are generally quick and low-cost since there is no need to heat the workpiece to high temperatures. Moreover, cold forged parts generally require minimal finishing compared to hot forged parts. In some embodiments, a generative machining process, such as CNC milling, is used to cut the recesses into the first surface.

[0056] The above description of the fasteners 10, drivers 34 and method is provided by way of example only and is not intended to be limiting upon the scope of the claimed invention.