GB2316989A

GB2316989A - A fastening device for one-way rotation

Info

Publication number: GB2316989A
Application number: GB9714143A
Authority: GB
Inventors: Donald John Hart
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-09-10
Filing date: 1997-07-07
Publication date: 1998-03-11
Also published as: GB9618849D0; GB9714143D0

Abstract

A fastening device 1 has a generally cone-shaped body with steps 7 formed in the sloping flank 6 of the body that face in one circumferential direction only. The steps 7 may be undercut, and may spiral from crown 2 to base 3 in the opposite circumferential direction. Such steps provide abutments for engaging a tool rotated in one direction, but providing no grip for a tool rotated in the opposite direction, thereby providing a fastening device that can not be undone. The device may have a central passage 4, 5 shaped to receive a conventional nut or bolt head, thereby adapting a conventional nut or bolt for rotation by a tool in one direction only. Alternatively the device may take the form of a nut or the head of a bolt. A socket spanner having a socket of complimentary shape to the fastening device 1 is also provided.

Description

I? Irovements relatinq to Fastening Devices" This invention relates to fastening devices, and it is particularly concerned with nuts and bolts or other items where the fastening action is rotary.

There are many situations where one wants a nut or a bolt, when done up tightly, to be virtually impossible to undo, short of destruction or severe mutilation.

It is the aim of this invention to provide such a device.

According to one aspect of the present invention there is provided a rotary fastening device, comprising a generally coned body with at least one step in the sloping flank between crown and base facing in one circumferential direction.

The step may be straight, in a radial plane coincident with the axis of the device, but preferably it will sweep at an angle from crown to base so that, in the other circumferential direction, (which is the way the device will be turned by a tool engaging the step) the base end of the step is forward of the crown end. The sweep may be straight or curved.

The step could be slightly undercut for a more positive grip by a tool, but with the forward sweep this may be unnecessary.

Preferably, there will be several steps, uni'firmly spaced around the device, and all facing in the same circumferential direction.

The device may be a nut or a bolt, in the latter case the coned body forming its head. Alternatively, it may be supplementary to a nut or a bolt head, having a co-axial passage wider at the crown than the base, the wide portion being shaped snugly to receive a nut or bolt head and the narrower portion the shank of a bolt. The wider portion will typically be hexagonal. Thus the device will act as a thick washer embracing the nut or bolt head, and when the device is turned so the nut or bolt will be turned.

According to another aspect of the present invention there is provided a socket spanner whose socket is shaped to be the inverse of the coned body of the device defined above.

For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a plan view of a rotary fastening device, Figure 2 is a side elevation of the device of Figure 1, and Figure 3 is a perspective view of that device.

The device has a generally frusto conical body 1 with a crown 2 and a base 3. The crown is formed with a hexagonal socket 4, and co-axially from the bottom of this an aperture 5 leads through to the base 3.

The flank of the body 1 is divided, in this example, into six equal sections 6. The transition between adjacent sections is a spiral step 7 starting at the crown 2 and sweeping in a curve down to the base 3, making the surface of the step convex but facing in one circumferential direction. This means that the main surface of each section 6 is not truly conical, but starts below the conic envelope defined by the tops of the steps 7 and inclines outwardly towards that envelope to reach it at the next step, in the manner of a countersink bit.

In use, a nut (not shown) is fitted snugly in the recess 4 and screwed on to a threaded bolt whose shank passes through the aperture 5. A socket spanner whose socket is the inverse of the shape of the body 1 is applied and turned in a clockwise direction as seen in Figure 1. The steps in the socket engage the steps 7 and the body 1 is rotated, carrying round the nut. The forward and downward sweep of the steps 7 (forwards being the direction of tightening) wedge the spanner down on the body 1, and the harder it is turned the firmer the engagement, and so although the steps 7 may be shallow, there is little chance of the spanner jumping off. However, as soon as it is reversed, the spanner is urged upwards by the screw effect of the sections 6, and it will click back over the steps 7 like a ratchet until it is turned back again in the forward direction, further to tighten the device.

Once the nut is tight, the spanner is quite ineffective for undoing the device, and the nut is inaccessible in the socket 4. The conical shape of the device makes it virtually impossible for any gripping device to achieve a firm hold: as a pair of jaws are brought together around it, they will simply slide off.

It will be understood that, instead of receiving a nut, the shank of a bolt may be passed down through the aperture 5 until the bolt head seats in the recess 4. The device is then used to turn the bolt.

Instead of having a device as complementary to a nut or bolt head, it could serve as such items. For example, to form a nut, there would be no recess 4, but an aperture 5 would extend through from crown to base and be screw threaded.

Claims

1. A rotary fastening device including a generally coned body with at least one step in the sloping flank between crown and base facing in one circumferential direction.

2. A rotary fastening device as claimed in Claim 1, wherein the step sweeps at an angle from crown to base so that, in the opposite circumferential direction, the base end of the step is forward of the crown end.

3. A rotary fastening device as claimed in Claim 1 or 2, wherein the step is undercut.

4. A rotary fastening device as claimed in any preceding Claim, wherein there is a plurality of such steps, all facing in the same circumferential direction and uniformly spaced around the axis of the device.

5. A rotary fastening device as claimed in any preceding Claim, wherein the device is a nut.

6. A rotary fastening device as claimed in any one of Claims 1 to 4, wherein the device is a bolt, the coned body forming its head.

7. A rotary fastening device as claimed in any one of Claims 1 to 4, wherein the device has a co-axial passage wider at the crown than the base, the wider portion being shaped snugly to receive a nut or bolt head and the narrower portion the shank of a bolt.

8. A rotary fastening device substantially as hereinbefore described with reference to the accompanying drawing.

9. A socket spanner whose socket is shaped to be the inverse of the coned body of the device as claimed in any preceding claim.