GB2037390A - Fixing device and tool therefor - Google Patents

Abstract

A security fixing device comprises a threaded portion 2 and a head portion 1. A blind aperture 4 is formed in the head, this aperture being offset from the axis 5 of the device. In order to rotate the device in order to secure or release same, a hand tool of complementary shape is provided. The tool comprises a head portion 6 in which is formed a shallow aperture 8 having an offset pin 9 extending from the bottom thereof for co-operation with the bore 4. Application of the invention to a nut and to a grub screw is also described. <IMAGE>

Description

SPECIFICATION Improvements in fixing device and tool therefore This invention relates to improvements in fixing devices and to fixing tools therefore.

It is frequently the case that fixing devices, for example screws and bolts, need to be resistant to tempering. This need can arise as a result of safety or security considerations, or both. Many tamper-proof fixing devices on the market are complex and, as a result, costly and there is therefore a tendency to use them only where the safety or security considerations outweigh the cost consideration.

It is an object of this invention to provide a tamper-proof fixing device which is cheap and can therefore be used for every fixing where safety or security is a problem.

According to a first aspect of the invention there is provided a fixing device comprising a body having an axis and being formed with a thread for use in securement of the device and means whereby the body may be rotated in order to secure or release the device, said means comprising, on an outer surface of the body a projection or aperture whose axis is parallel to and offset from that of the body.

The fixing device may take the form of a bolt or screw, in which case the thread is formed on the shank of the bolt or screw and said rotating means is formed on the head of the bolt or screw. Usually, the head is circular, and may have an outer surface which is flat, for example as in a countersunk head, or raised, for example as in a raised countersunk head, or spherical. The exact shape and configuration of the head will be dictated by the circumstances of use and in particular the manner in which the associated tool will be used to secure and release the device. Clearly, it is desirable that the head is of fairly low profile with respect to the surface into which the device is fixed since otherwise unauthorised removal will be readily possible using pliers or like implement.On the other hand, as will become clear later, it is at present anticipated that the device will have to protrude by a small amount above the surface in order to enable authorised removal of the device by means of a special tool designed for the purpose.

Alternatively, the fixing device may take the form of a grub screw (i.e. without a head) or a nut.

Both conventional nuts and blind nuts may be susceptible to the teachings of this invention, and specific embodiments of both types are described later.

The projection or aperture may be of any convenient shape, and its size may be small or large in relation to the overall width of the body, provided always that it is offset from the centre of the axis of the body. In the case of an aperture, this is preferably of circular cross section to discourage the unauthorised use of screwdrivers or like flat implements to open the device.

Preferably also, the amount of offset of the projection or aperture is small in relation to the size of the body since, the nearer the projection or aperture is to the axis of the body, the greater the leverage required to rotate the device. It is intended that authorised rotation of the fixing device will be facilitated by the use of a special tool.

Thus, in accordance with a second aspect of this invention, there is provided a tool for securing or releasing the fixing device according to the first aspect of the invention, said tool comprising an operating member having first means for engaging an edge of the body of the fixing device, second means for engaging said projection or aperture and means for rotating said operating member to thereby rotate the fixing device to secure or release the same. Said rotating means may comprise a source of power such as pneumatic power or an electric motor or, in the event that the tool is hand-operated, may comprise'a handle which is gripped to turn the tool.

Clearly the exact construction of the tool will depend upon the configuration of the fixing device with which it is to be used. For example, in one preferred embodiment of the invention, said first engaging means comprises the interior circumferential edge surface of a hollowed-out portion of said operating member. The hollowed portion is sized and shaped to loosely fit over the body of the fastening device and thus engage the same when the tool is rotated. If the body of the fixing device, and hence the shape of the holl9wed portion, is circular, then engagement between the two takes place by virtue of the offset of the projection/aperture when itself engaged by said second engaging means during rotation of the tool.

In order that the invention may be better understood, several embodiments thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a side view of a bolt according to the invention and an associated toot therefor; Figure 2 is a plan view of the bolt of Figure 1; Figures 3 and 4 are views similar to Figures 1 and 2 respectively, showing another embodiment of a bolt according to the invention; Figures 5 and 6 are views similar to Figures 1 and 2 respectively showing a nut according to the invention; Figure 7 is a side sectional view of a blind nut according to the invention; and Figures 8 and 9 are views similar to Figures 1 and 2 respectively showing a grub screw according to the invention.

Referring to Figures 1 and 2, there is shown a bolt comprising a disc-shaped head 1 and threaded shank 2. The head of the bolt may instead by any of the conventional shapes, but should possess two properties as follows: 1. It should not present too great a profile above the surface into which the bolt is fixed since otherwise unauthorised removal will be possible using readily available pliers or pincers; 2. It must protrude above the surface by a small amount in order to allow purchase of a suitable tool against the edge of the head during authorised removal.

The outwards facing surface 3 of the head 1 is formed with a circular blind bore 4 which is offset from the centre axis 5 of the shank 2. Clearly, the bore 4 must be positioned so that it cannot interfere with the threaded part of the shank.

A tool suitable for removal and replacement of the bolt is shown in Figure 1. The tool comprises a hand grip (not shown) to which is attached a stem (also not shown) the bottom of which is formed with an enlarged cylindrical portion 6. The lower face of the cylindrical portion 6 is formed with a low peripheral annular wall 7 which defines a shallow circular trough 8. The bottom of the trough 8 is formed with an upstanding circular projection 9. The size and disposition of the trough 8 and projection 9 are such that they are an exact complement to the head 1 of the bolt.

In order to rotate the bolt, the tool is brought down over the head of the bolt so that the head fits into the trough 8 and the projection 9 fits into the bore 4. Rotation of the tool thus causes a moment of force to be applied to the bolt by virtue of the offset of the interlocking bore 4/projection 9. Turning effort results from reaction between this interlocking bore/-projection and the interlocking effect of the wall 7 on the outer peripheral edge of the bolt head 1. However unauthorised removal of the bolt is difficult due to the small amount of offset which is present between the bore 4 and the centre axis of the head - a considerable force would be needed, for example to chisel the bolt out, and destruction of the bolt, rather than its removal, may be more likely to resultfrom such an attempt.

Figures 3 and 4 show another embodiment of the bolt of this invention. The bolt is similar to that of Figures 1 and 2, and identical reference' numerals have been used where appropraite. The difference lies in the fact that a projection 10, rather than an aperture, is formed on the head 1 of the bolt and in the fact that the projection has a considerably larger diameter, in relation to that of the head, than that of the bore 4 of Figures 1 and 2. As before, the projection 10, which is of circular configuration is offset from the axis 5 of the bolt, thus enabling a turning moment to be applied by means of an appropriately shaped tool, shown in Figure 3. The bottom of the trough 8 is formed with a short circular blind bore 11 corresponding in size and position with the projection 10.

Authorised removal and replacement of the bolt is carried but in a similar manner to that described above. The enlarged projection 10 enables greater torque to be applied to the bolt without the danger of breakage.

Figures 5 and 6, to which reference will now be made, shows the application of the invention to a nut 12 having an internally threaded throughaperture 13. The external shape of the nut is cylindrical with a circular section (to prevent spanners being employed) and defines a top wall 14 on which a projection 1 5 is formed. The projection' 5 is offset from the centre axis 1 6 of the nut so as to enable a turning moment to be applied to the nut by means of the tool shown in Figure 5. The tool is of similar configuration to that shown in Figure 3, and operates in the same manner. The cylindrical portion 6 is, however, formed with an axial bore 17 to allow a bolt (not shown) to be threaded through the nut.

Figure 7 shows one example of the application of the invention to a blind nut 18 having an internally threaded portion 19. The top wall 20 of the nut 18 is formed with an offset blind bore 21 in a similar manner to the bore 4 of the bolt of Figures 1 and 2. The nut is made generally cylindrical in shape and is thus difficult, if not impossible, to remove with conventional tools. A tool similar to that shown in Figure 1 can, however, be used to rotate the nut during authorised removal and replacement.

Figures 8 and 9, to which reference will now be made, show the application of the invention to a headless bolt, or grub screw, shown under reference 22. The screw has a threaded shank 23 defining a substantially flat surface 24 at one end thereof in which is formed a stepped blind bore.

The blind bore is formed in two sections: an outer section 25 which is concentric with the centre axis 26 of the screw, and an inner section 27 which is offset from that axis. For convenience, and in order to increase the difficulty of unauthorised removal, both sections 25 and 27 are circular in shape. The tool used for rotating the grub screw is shown in Figure 8 under reference 28.

The tool comprises a handle (not shown) from which extends a circular-section shaft 29 whose outside diameter corresponds with that of the outer section 25 of the blind bore. The end of shaft 29 is formed with an off-centre projection 30 which is circular, and is of such size as to fit inside the inner section 27 of the blind bore. To use the tool, the end of shaft 29 is inserted in the blind bore such that projection 30 enters the inner section 27. Rotation of the shaft 29 then causes the screw to rotate due to reaction between the offset projection 30 and inner section 27.

Claims (15)

1. A fixing device comprising a body having an axis and being formed with a thread for use in securement of the device and means whereby the body may be rotated in order to secure or release the device, said means comprising, on an outer surface of the body a projection or aperture whose axis is parallel to and offset from that of the body.

2. A fixing device as claimed in Claim 1 wherein the offset of said projection or aperture is small in order to hinder unauthorised removal of the device.

3. A fixing device as claimed in either of Claims 1 or 2 wherein the width of the projection or aperture is small in relation to the width of the body.

4. A fixing device as claimed in either of Claims 1 or 2 wherein the width of the projection or aperture is large in relation to the width of the body.

5. A fixing device as claimed in any one of Claims 1 to 4 wherein the sectional shape of the body in a plane orthogonal to the axis of the body is circular.

6. A fixing device as claimed in any one of Claims 1 to 5 wherein the projection or aperture is of circular shape.

7. A fixing device as claimed in any one of the preceding claims which takes the form of a screw or bolt having a head portion and a shank portion, and wherein the thread is formed on the shank portion, and said rotating means is formed on the head portion.

8. A fixing device as claimed in any one of Claims 1 to 6 which takes the form of a nut having a through aperture carrying said thread.

9. A fixing device as claimed in any one of Claims 1 to 6 which takes the form of a nut having a blind aperture carrying said thread.

10. A fixing device as claimed in any one of Claims 1 to 6 which takes the form of a grub screw having a shank carrying the thread, and wherein said projection or aperture is formed on or in one end of said screw.

11. A fixing device as claimed in Claim 10 wherein said rotating means comprises a projection or aperture which is stepped to form a first section which lies on the axis of the shank and a second section offset from that axis.

12. A fixing device substantially as hereinbefore described with reference to the accompanying drawings.

1 3. A tool for securing or releasing the fixing device as claimed in any one of the preceding claims, said tool comprising an operating member having first means for engaging an edge of the body of the fixing device, second means for engaging said projection or aperture and means for rotating said operating member to thereby rotate the fixing device to secure or release the same.

14. A tool as claimed in Claim 13 wherein said means for rotating said operating member comprises a handle which may be gripped to turn the tool.

15. A tool as claimed in either one of Claims 13 or 14 wherein said first engaging means comprises the interior circumferential edge surface of a hollowed-out portion of said operating member, said hollowed-out portion being sized and shaped to loosely fit over the body of the fastening device and thus engage the same when the tool is rotated.

1 6. A tool substantially as hereinbefore described with reference to the accompanying drawings.