Patent Description:
Screws and bolts which cannot be removed using standard spanner wrenches and flat blade, Phillips and hex-key drivers are used to prevent theft, vandalism and access to electrical and electronic components. Such tamper-proof screw and bolt heads have a design comprising recesses, or sockets, which mate with a corresponding security drive bit, like a key in a lock. In the absence of the correct security drive bit, the screw or bolt cannot be removed without drilling, chiseling or other obvious tampering methods.

A problem arises where existing security bits nonetheless become widely available, making it easy for unauthorised persons to remove the screws/bolts. There thus exists a need for a security fastener which cannot be removed using available tools and which is simple and inexpensive to manufacture.

<CIT> relates to a screw having a head with a segment shaped recess.

According to a first aspect of the invention, there is provided a security fastener for use with a corresponding driver according to claim <NUM>, the fastener comprising: a shank defining a longitudinal centre axis; and a head having a face for mating with a security bit of the driver, the face including at least one recess for receiving a corresponding projection of the bit, wherein the head has: <NUM>-fold rotational symmetry about the longitudinal centre axis of the shank; and a maximum of <NUM> 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. The head has a periphery and each of the at least one recesses is open at the periphery of the head. Since the recesses pass through the longitudinal centre axis, the recesses may be made open at the periphery of the head. This provides the recesses with a "free-draining" quality and means that the recesses are less prone to trapping dirt particles which might interfere with engagement between the head and the security bit.

The fact that the longitudinal centre axis intersects the first surface, and not one of the recesses, means that, unlike standard fasteners (such as Phillips screw head and Torx® screw head), the fastener head is not engaged at the centre of the head. This means that the head must be engaged on opposing sides of the longitudinal centre axis to apply sufficient torque to the head to rotate the fastener. However, the low degree of symmetry of the recesses on the face (the face has <NUM>-fold mirror symmetry, and <NUM>-fold rotational symmetry only) in turn makes it difficult for standard tools to engage the head using opposing surfaces. Thus, removal of the fastener is restricted to those in possession of a suitable driver which can engage the head on opposing sides.

Optionally, the at least one recess comprises a plurality of recesses. Additionally or alternatively, the face has a first side and an opposing second side, wherein each of the recesses extends only on one of the first and second sides. This feature makes it difficult for sufficient torque to be applied to the head to rotate the fastener by engaging only a single recess. However, the low degree of symmetry of the head makes it difficult for more than one recess to be engaged without a specially designed security bit.

Optionally, 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 any one of the at least one recesses is formed by an engagement surface, said engagement surface being parallel to the longitudinal centre axis. Forming the recess with perpendicular engagement surfaces avoids the need for sloped surfaces which complicate the manufacturing process, for instance when using techniques such as milling. Perpendicular engagement surfaces also reduce the tendency of the driver to slip, or "cam", out of the recess when torque is applied.

Optionally, 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. The term "single straight line" is used here to mean a single straight line of constant gradient. Accordingly, the interface between the first and second surfaces describes no corners or change of radius, greatly simplifying manufacture. This feature also means the fastener can be easily manufactured using simple techniques such as milling using a single cylindrical milling tool.

Optionally, 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 centre axis. Accordingly, the head presents no parallel opposing engagement surfaces. This makes it difficult to apply sufficient force to the engagement surfaces to rotate the fastener by gripping the engagement surfaces using a gripping tool such as pliers.

In some embodiments, 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. The combination of one arcuate engagement surface and one flat surface provides good engagement between the driver and the fastener whilst allowing for asymmetry and easy manufacture. Optionally, the first recess and the second recess are arranged diametrically opposite one another on the head. This arrangement makes it difficult to apply sufficient torque to the fastener to rotate the same by gripping the engagement surfaces using a gripping tool, such as a pliers. This is because tools with flat surfaces are unable to achieve good contact with the arcuate engagement surface.

In some embodiments, 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. Further optionally, the third recess is substantially a mirror image of the first recess, the mirror plane containing the longitudinal centre axis.

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

Referring to <FIG>, a fastener <NUM> according to a first embodiment of the present invention comprises a head <NUM> and a shank <NUM>. The shank <NUM> defines a longitudinal centre axis <NUM> and preferably comprises a threaded portion <NUM> which may extend along the full length of the shank <NUM>. Alternatively, as illustrated in <FIG>, the shank <NUM> may include a threaded portion <NUM> and a non-threaded portion <NUM>. The head <NUM> 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 <NUM>, the face defines a circular periphery <NUM>. The face includes a first surface <NUM> and first and second recesses <NUM>,<NUM> defined within the first surface <NUM>. Each of the first and second recesses <NUM>,<NUM> is open at the periphery <NUM> of the head.

Each of the first and second recesses <NUM>,<NUM> is defined by an indented, or recessed, surface within the first surface <NUM>. The transition between the indented surface of the first recess <NUM> and the first surface <NUM> comprises a wall defining a first engagement surface <NUM> that extends parallel to the longitudinal centre axis <NUM>. The transition between the indented surface of the second recess <NUM> and the first surface <NUM> comprises a wall defining a second engagement surface <NUM> that extends parallel to the longitudinal centre axis <NUM>.

It will of course be appreciated that whilst the particular embodiment shown in <FIG> is provided with two recesses, other embodiments may include only a single recess or include more than two recesses.

In the embodiment shown in <FIG>, when viewed along the longitudinal centre axis <NUM>, the first engagement surface <NUM> between the first surface <NUM> and the first recess <NUM> describes an arc which intersects the circular periphery of the face of the head <NUM> at first and second points on the periphery <NUM>, such that the first recess <NUM> comprises a lens shape. The arc described by the first engagement surface <NUM> preferably has a smaller radius than the radius of the circular periphery of the face, such that the first recess <NUM> has as an asymmetric lens shape.

The second engagement surface <NUM> is substantially flat, or planar. As such, when viewed along the longitudinal centre axis <NUM>, the second engagement surface <NUM> describes a chord of the face, such that the second recess <NUM> has a segment shape.

The first <NUM> and second <NUM> 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 <NUM> and second recesses <NUM>.

Referring to <FIG>, a driver <NUM> for installing and removing the fastener <NUM> according to the first embodiment comprises a handle <NUM> and a security bit <NUM> configured to mate with the face of the fastener <NUM>, as will be described in more detail below. The security bit <NUM> defines a longitudinal centre axis <NUM> and includes first and second projections <NUM>,<NUM> which extend along a direction parallel to the longitudinal centre axis <NUM>, and which correspond respectively to the first <NUM> and second <NUM> recesses of the fastener <NUM>.

Referring in particular to <FIG>, the first projection <NUM> has a form which is complementary to the first recess <NUM> of the fastener <NUM>, and comprises a first driving surface <NUM> which extends parallel to the longitudinal centre axis <NUM> of the driver, and a first distal surface <NUM> which extends perpendicular to said longitudinal centre axis <NUM>. The first distal surface <NUM> comprises an asymmetric lens shape which is congruent with the asymmetric lens shape of the first recess <NUM>.

The second projection <NUM> has a form which is complementary to the second recess <NUM> of the fastener <NUM>, and comprises a second driving surface <NUM> which extends parallel to the longitudinal centre axis <NUM> of the driver, and a second distal surface <NUM> which extends perpendicular to said longitudinal centre axis <NUM>. The second distal surface <NUM> comprises a segment shape which is congruent with the segment shape of the second recess <NUM>.

In use, the fastener <NUM> of the second embodiment is installed or removed in a hole or bore in an object by rotating the fastener <NUM> using the driver <NUM>. The bit <NUM> of the driver <NUM> is mated with the face of the head <NUM> by engaging the first and second projections <NUM>,<NUM> in the first and second recesses <NUM>,<NUM>, respectively. In this configuration, the first driving surface <NUM> of the first projection <NUM> is engaged with the first engagement surface <NUM> of the first recess <NUM>, the second driving surface <NUM> of the second projection <NUM> is engaged with the second engagement surface <NUM> of the second recess <NUM>. An operator then rotates the driver <NUM> in the appropriate direction using the handle <NUM>. Torque is transferred to the fastener <NUM> through the driving surfaces <NUM>,<NUM> to the engagement surfaces <NUM>,<NUM> causing the fastener <NUM> to rotate to either insert or remove the fastener, as desired.

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 <NUM> to rotate the fastener, torque must be applied to each of the first and second engagement surfaces <NUM>,<NUM>. As such, only a tool having a shape capable of mating with both recesses <NUM>,<NUM>,<NUM> will be able to remove the fastener <NUM>. Due to the low degree of symmetry of the recesses on the face (the face has <NUM>-fold mirror symmetry, and <NUM>-fold rotational symmetry only), standard tools are unable to engage both recesses <NUM>,<NUM> simultaneously. Thus, removal of the fastener is restricted to those in possession of the driver <NUM>.

It will also be appreciated that the use of an arcuate engagement surface, as in the first recess <NUM>, in opposing relationship with the planar engagement surface of the second recess <NUM> 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 <NUM> by gripping the engagement surfaces using a gripping tool such as a wrench.

Referring to <FIG>, a fastener <NUM> 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.

The second embodiment of the fastener <NUM> comprises a head <NUM> having a face which includes a first surface <NUM> and first, second and third recesses <NUM>,<NUM>,<NUM>. The transition between the indented surface of the first recess <NUM> and the first surface <NUM> comprises a wall defining a first engagement surface <NUM> that extends parallel to the longitudinal centre axis <NUM> of the fastener <NUM>. The transition between the indented surface of the second recess <NUM> and the first surface <NUM> comprises a wall defining a second engagement surface <NUM> that extends parallel to the longitudinal centre axis <NUM>. The transition between the indented surface of the third recess <NUM> and the first surface <NUM> comprises a wall defining a third engagement surface <NUM> that extends parallel to the longitudinal centre axis <NUM>.

The first engagement surface <NUM> between the first surface <NUM> and the first recess <NUM> is substantially flat, or planar. As such, when viewed along the longitudinal centre axis <NUM>, the first engagement surface <NUM> describes a chord of the face, such that the first recess <NUM> has a segment shape.

The second engagement surface <NUM> describes an arc which intersects the circular periphery <NUM> of the face of the head <NUM> at first and second points on said periphery, such that the second recess <NUM> comprises a lens shape. The arc described by the second engagement surface <NUM> has a smaller radius than the radius of the circular periphery <NUM> of the face, such that the second recess <NUM> has as an asymmetric lens shape.

The third engagement surface <NUM> between the first surface <NUM> and the third recess <NUM> is substantially flat, or planar. As such, when viewed along the longitudinal centre axis <NUM>, the third engagement surface <NUM> describes a chord of the face, such that the third recess <NUM> has a segment shape. The chord described by the third engagement surface <NUM> has a length which is substantially the same as the length of the chord described by the first engagement surface <NUM>.

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

Referring to <FIG>, a driver <NUM> for installing and removing the fastener <NUM> according to the second embodiment comprises a security bit <NUM> including first, second and third projections <NUM>,<NUM>,<NUM> which each project along a direction parallel to the longitudinal centre axis <NUM> of the bit <NUM>. The first, second and third projections <NUM>,<NUM>,<NUM> correspond respectively to the first, second and third recesses <NUM>,<NUM>,<NUM> of the fastener <NUM> and are disposed in spaced angular relationship around the longitudinal centre axis <NUM> of the bit <NUM>.

The first projection <NUM> has a form which is complementary to that of the first recess <NUM> of the fastener <NUM>, and comprises a first driving surface <NUM> which extends parallel to the longitudinal centre axis <NUM> of the driver, and a first distal surface <NUM> which extends perpendicular to said longitudinal centre axis <NUM>. The first distal surface <NUM> comprises a segment shape which is congruent with the segment shape of the first recess <NUM>.

The third projection <NUM> has a form which is complementary to that of the third recess <NUM> of the fastener <NUM>, and comprises a third driving surface <NUM> which extends parallel to the longitudinal centre axis <NUM> of the driver, and a third distal surface <NUM> which extends perpendicular to said longitudinal centre axis <NUM>. The third distal surface <NUM> comprises a segment shape which is congruent with the segment shape of the third recess <NUM>. The third projection <NUM> is a mirror image of the first projection <NUM> through a mirror plane containing the longitudinal centre axis <NUM>.

The second projection <NUM> has a form which is complementary to that of the second recess <NUM> of the fastener <NUM> and comprises a second driving surface <NUM> which extends parallel to the longitudinal centre axis <NUM> of the driver, and a second distal surface <NUM> which extends perpendicular to said longitudinal centre axis <NUM>. The second distal surface <NUM> comprises an asymmetric lens shape which is congruent with the asymmetric lens shape of the second recess <NUM>.

In use, the fastener <NUM> of the second embodiment is installed in a hole or bore in an object by rotating the fastener <NUM> using the driver <NUM> of the second embodiment. The bit <NUM> of the driver <NUM> is mated with the face of the head <NUM> by engaging the first, second and third projections <NUM>,<NUM>,<NUM> in the first, second and third recesses <NUM>,<NUM>,<NUM>, respectively. In this configuration, the first driving surface of the first projection is engaged with the first engagement surface <NUM> of the first recess <NUM>, the second driving surface <NUM> of the second projection is engaged with the second engagement surface of the second recess, and the third driving surface <NUM> of the third projection <NUM> is engaged with the third engagement surface of the third recess. An operator then rotates the driver <NUM> using the handle <NUM>. Torque is transferred to the fastener <NUM> through the driving surfaces <NUM>,<NUM>,<NUM> to the engagement surfaces <NUM>,<NUM>,<NUM> causing the fastener <NUM> to rotate. As the fastener <NUM> rotates the right-handed thread pulls the fastener <NUM> into the hole/bore. The driver <NUM> is then rotated until the fastener <NUM> bears against the surface of the object.

To remove the fastener <NUM>, the bit <NUM> is again mated with the driver <NUM> by engaging the first, second and third projections <NUM>,<NUM>,<NUM> in the first, second and third recesses <NUM>,<NUM>,<NUM>, respectively and the driver <NUM> rotated in the opposite direction.

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 <NUM> to rotate the same, torque must be applied to each of the first second and third engagement surfaces <NUM>,<NUM>,<NUM>. As such, only a tool having a shape capable of mating with all three recesses <NUM>,<NUM>,<NUM> will be able to remove the fastener <NUM>. Due to the low symmetry of the recesses on the face (the face has <NUM>-fold mirror symmetry, and <NUM>-fold rotational symmetry only), standard tools are unable to engage each of the recesses <NUM>,<NUM>,<NUM>. Thus removal of the fastener is restricted to those in possession of the driver <NUM> of the second embodiment.

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 <NUM> by gripping the engagement surfaces <NUM>,<NUM>,<NUM> using a gripping tool such as a wrench.

A method of manufacturing a security fastener as illustrated in the previous figures will now be described with reference to <FIG>.

Referring in particular to <FIG>, a first step of the method comprises providing a preform <NUM>' of the fastener. The preform <NUM>' comprises a shank <NUM> defining a longitudinal centre axis <NUM> and a head <NUM>' having a first surface facing along the longitudinal centre axis <NUM>. The first surface <NUM> has a circular periphery <NUM> and a first side <NUM> and an opposing second side <NUM>.

Still referring to <FIG>, a second step of the method comprises cutting a first recess <NUM> into the first side <NUM> of the first surface of the head <NUM>'. Preferably, the recesses are cut into the first surface by milling the head <NUM>' using a rotary cutter <NUM>.

To cut the first recess <NUM> into head <NUM>', the rotary cutter <NUM> is translated in a first radial direction D1 to move the cutter <NUM> partially into the head <NUM>' through the periphery of the head <NUM>'. 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 <NUM> of the head, as shown in <FIG>.

The transition between the indented surface of the first recess <NUM> and the first surface <NUM> comprises a first engagement surface <NUM> that extends parallel to the longitudinal centre axis. When viewed along the longitudinal centre axis <NUM>, the first engagement surface <NUM> is described by an arc having a radius equal to the radius of the cylindrical cutter.

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

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.

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