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Title:
LENGTH AJUSTABLE TORQUE BAR EXTENSION
Document Type and Number:
WIPO Patent Application WO/2005/070621
Kind Code:
A1
Abstract:
An extendible coupling device (10) for transmitting a torque from a torque input member to a torque output member, the device comprising a plunger (12), an elongate body (14) in which the plunger (12) is movable between retracted and extended positions, and an adjustment mechanism (16) that may be adjusted. to permit movement of the plunger (12) between the retracted and extended positions, the body (14) having coupling means (38) for coupling to one of the torque members, the plunger having coupling means (28) for coupling to the other torque member, and the plunger (12) having engagement means (24) that is engageable with a co-operating portion (32, 40) of the body so as substantially to prevent rotation of the plunger relative to the body, wherein the adjustment mechanism is disposed inside the body.

Inventors:
Smith, Anthony Charles Rust c/o Auto, Electrical Rescue (Unit 2 Jubilee Work, Clavering Essex CB11 4WA, GB)
Application Number:
PCT/GB2005/000221
Publication Date:
August 04, 2005
Filing Date:
January 24, 2005
Export Citation:
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Assignee:
Smith, Anthony Charles Rust c/o Auto, Electrical Rescue (Unit 2 Jubilee Work, Clavering Essex CB11 4WA, GB)
International Classes:
B25B13/48; B25B23/00; (IPC1-7): B25B23/00; B25B13/48
Foreign References:
US20010044989A12001-11-29
US4754670A1988-07-05
US20020178874A12002-12-05
GB1348814A1974-03-27
Attorney, Agent or Firm:
Lipscombe, Martin John (Keith W Nash & Co, 90-92 Regent Street, Cambridge CB2 1DP, GB)
Download PDF:
Claims:
Claims
1. An extendible coupling device for transmitting a torque from a torque input member to a torque output member, the device comprising a plunger, an elongate body in which the plunger is movable between retracted and extended positions, and an adjustment mechanism that may be adjusted to permit movement of the plunger between the retracted and extended positions, the body having coupling means for coupling to one of the torque members, the plunger having coupling means for coupling to the other torque member, and the plunger having engagement means that is engageable with a cooperating portion of the body so as substantially to prevent rotation of the plunger relative to the body, wherein the adjustment mechanism is disposed inside the body.
2. A device according to claim 1, wherein the adjustment mechanism is adjustable between a first condition in which the plunger is movable between the retracted and extended positions, and a second condition in which the plunger is prevented from moving between the retracted and extended positions.
3. A device according to claim 1, wherein the adjustment mechanism prevents the plunger from moving between the retracted and extended positions and adjustment of the adjustment mechanism moves the plunger between the retracted and extended positions.
4. A device according to any preceding claim, wherein adjustment of the adjustment mechanism does not allow ingress of dirt or small particulate material into the body of the device.
5. A device according to any preceding claim, wherein the adjustment mechanism may be adjusted from a region of the device in the vicinity of the coupling means for coupling to the torque input member.
6. A device according to claim 5, wherein the adjustment mechanism may be adjusted from a region of the device inside the coupling means for coupling to the torque input member.
7. A device according to any preceding claim, wherein the coupling means of the body comprises a socket for coupling to a stub of a torque member.
8. A device according to any preceding claim, wherein the coupling means of the plunger comprises a stub for coupling to a socket of a torque member.
9. A device according to claim 8 when dependent from claim 7, wherein the extendible coupling device comprises an extender bar, the coupling means of the body comprising a socket for coupling to a stub of a ratchet tool and the coupling means of the plunger comprising a stub for coupling to a socket of a socket spanner.
10. A device according to claim 9, wherein the adjustment mechanism is adjustable from the socket.
11. A device according to any preceding claim, wherein the engagement means of the plunger comprises an external surface of the plunger.
12. A device according to any preceding claim, wherein the cooperating portion of the body comprises an internal surface of the body.
13. A device according to claim 12 when dependent from claim 11, wherein the plunger has a portion of polygonal cross section for engagement with the internal surface of the body.
14. A device according to claim 13, wherein the plunger has a portion of hexagonal cross section for engagement with the internal surface of the body.
15. A device according to claim 13 or 14, wherein the plunger also has an intermediate portion between the portion of polygonal cross section and the coupling means, the intermediate portion having a smaller crosssectional area than the portion of polygonal cross section.
16. A device according to claim 15, wherein the intermediate portion is of cylindrical cross section.
17. A device according to any preceding claim, wherein the body, plunger and/or adjustment mechanism is provided with a stop to define the extended position of the plunger relative to the body.
18. A device according to any preceding claim, wherein the plunger is provided with indicator means for indicating when the plunger is in a furthest recommended extended position relative to the body.
19. A device according to claim 18, wherein the portion of polygonal cross section of the plunger is formed with notches towards its distal end, which notches are concealed by the body when the plunger is in the retracted position, and visible when the plunger is in a furthest recommended extended position relative to the body.
20. A device according to any preceding claim, wherein the body is generally cylindrical and defines a generally polygonal cavity for receiving the plunger.
21. A device according to claim 20, wherein the body defines a generally hexagonal cavity . for receiving the plunger.
22. A device according to claim 21, wherein the body defines a cavity in the form of a hexagon, the apices of which are marginally enlarged.
23. A device according to any preceding claim, wherein the body is provided with purchase means to facilitate turning of the body with one's fingers.
24. A device according to any preceding claim, wherein the locking mechanism comprises screw means operable to move the plunger between the extended and retracted positions.
25. A device according to claim 24, wherein the screw means comprises a screw, the shank of which is engageable with an axial tapped bore in the plunger.
26. A device according to claim 24 or 25, wherein the screw means is retained in the body.
27. A device according to claim 25 or 26, wherein the head of the screw is accessible through the socket of the body.
28. A device according to claim 25,26 or 27, wherein the axial bore is formed centrally in the plunger.
29. A device substantially as hereinbefore described and with reference to the accompanying drawings.
Description:
LENGTH ADJUSTABLE TORQUE BAR EXTENSION Field of the Invention This invention relates to an extendible coupling device for transmitting a torque from a torque input member to a torque output member, and in particular to an extendible coupling device in the form of an extender bar for transmitting a torque from a ratchet tool to a socket spanner.

Background to the Invention Extendible coupling devices in the form of extender bars attachable between a ratchet tool and a socket spanner to enable the socket spanner to be used in a confined space are well known.

United States Patents Nos. 4,703, 677,4, 102,375, 3,343, 434,4, 317,393 and 854,742, for example, all show extendible coupling devices for transmitting a torque from a torque input member to a torque output member, the devices comprising a plunger, an elongate body in which the plunger is movable between retracted and extended positions and an adjustment mechanism that may be adjusted to permit movement of the plunger between the retracted and extended positions, the body having coupling means for coupling to one of the torque members, the plunger having coupling means for coupling to the other torque member, and the plunger having engagement means that is engageable with a co-operating portion of the body so as substantially to prevent rotation of the plunger relative to the body.

The extendible coupling devices shown in these patents all have the adjustment mechanism at least partially disposed outside the body ; which is disadvantageous because it leaves the mechanism vulnerable to wear and jamming through intrusion of foreign bodies.

When using such an extendible coupling device in a confined space it is necessary frequently to adjust the length of the device by shortening the device as a nut or bolt is loosened or by lengthening the device as a nut or bolt is tightened. This is made difficult with the known devices because in a confined space the adjustment mechanism is unlikely to be easily accessible, situated as it is in either the side wall of the body or at the end of the body that receives the plunger.

Summary of the Invention According to the invention there is provided an extendible coupling device for transmitting a torque from a torque input member to a torque output member, the device comprising a plunger, an elongate body in which the plunger is movable between retracted and extended positions, and an adjustment mechanism that may be adjusted to permit movement of the plunger between the retracted and extended positions, the body having coupling means for coupling to one of the torque members, the plunger having coupling means for coupling to the other torque member, and the plunger having engagement means that is engageable with a co-operating portion of the body so as substantially to prevent rotation of the plunger relative to the body, wherein the adjustment mechanism is disposed inside the body.

The invention can provide an extendible coupling device of a more robust construction than known devices.

In one embodiment of the invention the adjustment mechanism is adjustable between a first condition in which the plunger is movable between the retracted and extended positions, and a second condition in which the plunger is prevented from moving between the retracted and extended positions.

In another embodiment of the invention the adjustment mechanism prevents the plunger from moving between the retracted and extended positions and adjustment of the adjustment mechanism moves the plunger between the retracted and extended positions.

Preferably adjustment of the adjustment mechanism does not allow ingress of dirt or small particulate material into the body of the device.

In preferred embodiments of the invention the adjustment mechanism is disposed entirely inside the body.

Preferably the adjustment mechanism may be adjusted from a region of the device in the vicinity of the coupling means for coupling to the torque input member.

Preferably the adjustment mechanism may be adjusted from a region of the device inside the coupling means for coupling to the torque input member.

Preferably the coupling means of the body comprises a socket for coupling to a stub of a torque member.

Preferably the coupling means of the plunger comprises a stub for coupling to a socket of a torque member.

In preferred embodiments of the invention the extendible coupling device comprises an extender bar, the coupling means of the body comprising a socket for coupling to a stub of a ratchet tool and the coupling means of the plunger comprising a stub for coupling to a socket of a socket spanner.

Where the extendible coupling device comprises an extender bar, the adjustment mechanism is preferably adjustable from the socket.

The invention can further provide an extendible coupling device in the form of an extender bar that may be adjusted in length in confined spaces more easily than known extender bars, because the adjustment mechanism is operable from the socket to which the ratchet tool is coupled.

Typically the stub of the plunger is provided with a spring-loaded ball bearing for engagement with a notch in a socket of a socket spanner, so as to retain the stub in couplement with the socket spanner.

The engagement means of the plunger may advantageously comprise an external surface of the plunger.

The co-operating portion of the body may advantageously comprise an internal surface of the body.

The plunger preferably has a portion of polygonal cross section for engagement with the internal surface of the body.

More preferably still, the plunger has a portion of hexagonal cross section for engagement with the internal surface of the body. The portion of hexagonal cross section enables a torque to be applied to the plunger by means of a suitably sized spanner engaged with the portion of hexagonal cross section.

The plunger may advantageously also have an intermediate portion between the portion of polygonal cross section and the coupling means, the intermediate portion having a smaller cross-sectional area than the portion of polygonal cross section. The intermediate portion enables a ring spanner to be disengaged from the portion of hexagonal cross section without the need for disengaging the plunger from the torque member. This is useful, for example, where a ring spanner has been used to turn the plunger to turn a socket spanner to loosen a nut or bolt to finger tightness, and it is desired to remove the nut or bolt by turning the body with one's fingers, rather than by means of the ring spanner.

In the preferred embodiments the intermediate portion is of cylindrical cross section, the cylindrical cross section providing mechanical strength whilst enabling the plunger to be rotated inside the ring of a ring spanner.

The body, plunger and/or adjustment mechanism may advantageously be provided with a stop to define the extended position of the plunger relative to the body.

Alternatively or additionally, the plunger may advantageously be provided with indicator means for indicating when the plunger is in a furthest recommended extended position relative to the body.

In the preferred embodiments the portion of polygonal cross section of the plunger is formed with notches towards its distal end, which notches are concealed by the body when the plunger is in the retracted position, and visible when the plunger is in a furthest recommended extended position relative to the body.

The notches provide an indication of the furthest recommended extension of the plunger relative to the body, whilst allowing the plunger to be removed from the body, for example for oiling or cleaning of the extendible coupling device.

The body may advantageously be generally cylindrical and define a generally polygonal cavity for receiving the plunger.

Preferably the body defines a generally hexagonal cavity for receiving the plunger.

In the preferred embodiments the body defines a cavity in the form of a hexagon, the apices of which are marginally enlarged. This ensures that, when a torque is applied to the body, there is a slight rotation of the body relative to the plunger, such that the flats of the portion of hexagonal cross section of the plunger, as opposed to the apices, engage with the internal surface of the body, thus reducing the shear stress to which the plunger is subjected in use.

Thus the object of the invention may be achieved by embodiments of the extendible coupling device of which the plunger has engagement means that is engageable with a co- operating portion of the body so as substantially to prevent rotation of the plunger relative to the body.

The body may advantageously be provided with purchase means to facilitate turning of the body with one's fingers.

In the preferred embodiments the purchase means is a splined portion.

The adjustment mechanism may advantageously comprise a key and an axial bore in the plunger for receiving the key, the key having at least one radially outwardly projecting tooth and the bore being formed with a plurality of radially outwardly directed recesses to accommodate the at least one tooth, and the adjustment mechanism being adjustable by rotation of the key relative to the plunger and body between a first position in which the plunger may be moved between the retracted and extended positions and a second position in which the at least one tooth is received in one of the plurality of recesses so as to prevent movement of the plunger between the retracted and extended positions.

Alternatively the adjustment mechanism may advantageously comprise a drive member, engagement means and an axial bore in the plunger for receiving the drive member and engagement means, the drive member being engageable with the engagement means and the bore being formed with a plurality of radially outwardly directed recesses to accommodate the engagement means, and the adjustment mechanism being adjustable by movement of the drive member relative to the body between a first position in which the drive member is disengaged from the engagement means and the plunger may be moved between the retracted and extended positions, and a second position in which the drive member engages with the engagement means and drives the engagement means into at least one of the plurality of recesses so as to prevent movement of the plunger between the retracted and extended positions.

Where the adjustment mechanism comprises the drive member and engagement means, the adjustment mechanism is preferably adjustable by movement of the drive member between retracted and extended positions relative to the plunger.

It will be appreciated that the aforementioned adjustment mechanisms can only lock the plunger in a finite number of positions relative to the body because of the finite number of recesses in the bore in which the tooth or engagement means can be received.

Preferably, therefore, the adjustment mechanism comprises first and second chambers and valve means movable between a first condition to permit fluid to flow between the chambers and a second condition to prevent fluid from flowing between the chambers, the first chamber being formed with an aperture in which the second chamber forms a sealing fit so as to be movable between extended and retracted positions relative to the first chamber with accompanying flow of fluid from one chamber to the other, the mechanism containing sufficient fluid to fill one of the chambers and the first chamber being attached to one of the plunger and the body and the second chamber being attached to the other.

Where the fluid is a gas, some movement of the second chamber relative to the first chamber is possible when the valve means is in the second position by means of compression and rarefaction of the gas.

Preferably, therefore, the fluid is a liquid. In that case, only movement of the second chamber from the retracted position to the extended position is possible when the valve means is in the second position.

Where the adjustment mechanism comprises the drive member and engagement means or first and second chambers and valve means, the device may advantageously further include a push button, preferably spring-loaded, operable to adjust the adjustment mechanism.

Where the device includes the push button, the push button may advantageously be located in a socket for receiving a stub of a ratchet tool.

The stubs of most ratchet tools are provided with a spring-loaded ball bearing for engagement with a notch in a socket of a socket spanner or extender bar, so as to retain the stub in couplement with the socket spanner or extender bar. The stubs of a few ratchet tools are provided with a ball bearing that projects from the stub as a result of enagagement with a spring-loaded pin that projects from the rear of the ratchet tool and passes through the length of the stub. In order to remove a socket spanner or extender bar from the stub of such a ratchet tool, the pin must be pressed into the rear of the ratchet. tool. Pressing the pin into the rear of the tool allows the ball bearing to retract into the stub so that the socket spanner or extender bar can be removed from the stub and also causes the opposite end of the pin to project from the end of the stub of the ratchet tool, which serves to dislodge the socket spanner or extender bar from the stub of the ratchet tool.

Where the push button is located in the socket for receiving the stub of the ratchet tool, the push button is preferably located such that pressing the pin of the ratchet tool operates the push button. With this arrangement the length of the extender bar can be adjusted without removing the ratchet tool from the socket of the extender bar.

In contrast with the first two adjustment mechanisms, the aforementioned adjustment mechanism can lock the plunger in any position relative to the body, albeit while permitting a small amount of movement of the plunger relative to the body.

More preferably still, therefore, the adjustment mechanism comprises screw means operable to move the plunger between the extended and retracted positions.

Preferably the screw means comprises a screw, the shank of which is engageable with an axial tapped bore in the plunger.

Preferably the screw means is retained in the body, preferably by a lock nut.

Preferably the head of the screw is accessible through the socket of the body.

The aforementioned adjustment mechanism can lock the plunger in any position relative to the body while permitting very little movement of the plunger relative to body without rotation of the screw means, and can be manufactured more cheaply than the previous adjustment mechanisms.

Where the plunger is formed with an axial bore, the axial bore is preferably formed centrally in the plunger. This has the advantage that, when the plunger is subjected to case-hardening, for example by cyanide-hardening, the molten sodium cyanide penetrates the bore and the plunger is thereby hardened both from the outside inwards and from the inside outwards.

Further according to the invention there is provided an extendible coupling device for transmitting a torque from a torque input member to a torque output member, the device comprising a plunger, an elongate body in which the plunger is movable between retracted and extended positions, and an adjustment mechanism that may be adjusted to permit movement of the plunger between the retracted and extended positions, the body having coupling means for coupling to one of the torque members, the plunger having coupling means for coupling to the other torque member, and the plunger having engagement means that is engageable with a co-operating portion of the body so as substantially to prevent rotation of the plunger relative to the body, wherein the adjustment mechanism may be adjusted by performing an operation on a part of the device in, on or substantially adjacent to the coupling means for coupling to the torque input means.

Preferably the adjustment mechanism may be adjusted by performing an operation on part of the device inside a socket for coupling to the torque input means.

For the avoidance of doubt it is hereby stated that any features described here as advantageous or preferable or the like may be used in the invention in isolation or in combination with any other feature or features so described, unless the context dictates otherwise.

Brief Description of the Drawings The invention will now be described, by way of example, with reference to the attached drawing figures in which: Figure 1 is a sectional view of a first extendible coupling device in accordance with the invention; Figure 2 is a perspective view of the extendible coupling device of Figure 1; Figure 3 is a perspective view of the plunger of the extendible coupling device of Figures 1 and 2; and Figures 4,5 and 6 are sectional views, respectively, of second, third and fourth extendible coupling devices in accordance with the invention.

Detailed Description of an Embodiment The extendible coupling device of Figure 1 is in the form of an extender bar 10 comprising a plunger indicated generally by reference numeral 12, a body indicated generally by reference numeral 14 and an adjustment mechanism in the form of a screw indicated generally by reference numeral 16.

The plunger 12 consists of an elongate case-hardened chromium-vanadium steel forging indicated generally by reference numeral 18, a helical compression spring 20 and a ball bearing 22.

The forging 18 has engagement means in the form of a base portion 24 that is of regular hexagonal cross section, and also has a cylindrical intermediate portion 26 and coupling means in the form of a stub 28 that is of square cross section for coupling to a socket of a torque output member in the form of a socket spanner (not shown), or another extension bar (not shown). The spring 20 and ball bearing 22 are retained in a hole 23 drilled in one of the four side faces of the stub 28, the spring serving to urge the ball bearing out of the hole and the mouth of the hole being narrowed using a punch so as to retain the ball bearing.

When the stub is coupled to a socket of another component, the ball bearing is urged by the spring into a notch inside the socket, so as to keep the stub in couplement to the socket.

The forging 18 has a central axial tapped hole 30, sized to receive an M5 thread of 0.8mm pitch, that is to say, one revolution of the thread will advance the thread by 0. 8mm along the hole.

The hole 30 continues for the entire length of the base portion 24 and for most of the intermediate portion 26, ending just before the stub 28.

The hole 30 in the base and intermediate portions and the hole 23 in the stub are formed, the spring 20 and ball bearing 22 are placed into the hole 23 and the hole narrowed before the plunger is case-hardened by cyanide dipping. This enables the molten sodium cyanide used in the dipping process to penetrate the holes 23 and 30 so as to harden the cores of the base and intermediate portions 24 and 26 and the core of the stub 28.

In addition to simplifying the machining of the plunger (which would otherwise involve machining hardened steel), case-hardening of the plunger both from the outside of the plunger inwards and from the inside of the plunger outwards greatly increases the mechanical strength of the plunger.

The body 14 is generally cylindrical, made of case-hardened chromium-vanadium steel and consists of a wide portion 32, purchase means in the form of a splined portion 34, and a narrow portion 36. The narrow portion 36 and splined portion 34 define coupling means in the form of a square socket 38 for coupling to a stub of a torque input member in the form of a ratchet tool (not shown) and the wide portion 32 defines a co-operating portion in the form of a generally hexagonal cavity 40 with which the hexagonal base portion of the plunger is engageable. The socket 38 and cavity 40 are substantially separated by a partition 42, however a central hole in the partition 42 links the socket 38 and cavity 40.

The central hole is sized to receive the shank of an M5 screw.

The screw 16 is a hardened chromium-molybdenum steel M5 screw with an 0.8mm thread pitch for engagement with the tapped hole 30 in the plunger 12. The screw is disposed in the body through a mild steel washer 44 such that the washer 44 abuts the partition 42 and the head 46 of the screw abuts the washer, the head 46 of the screw being accommodated in the square socket 38 and the shank 48 of the screw projecting through the hole in the partition into the generally hexagonal cavity 40.

The shank of the screw passes through a further mild steel washer 50, which abuts the opposite side of the partition to the washer 44, and the head 46 of the screw is maintained in abutment with the washer 44 by a lock nut 52 that is tightened onto the shank 48 of the screw into abutment with the washer 50. The head 46 of the screw has a cross-shaped slot enabling the screw to be turned relative to the body by means of a Phillips (TM) screwdriver.

The extender bar is assembled by introducing the hexagonal base portion 24 of the plunger 12 into the generally hexagonal cavity 40 of the body 14 until the shank of the screw 16 engages with the tapped hole 30 of the plunger. Clockwise rotation of the screw head 46 (as seen from above) relative to the body then draws the plunger into the body and anticlockwise rotation of the screw head drives the plunger out of the body.

Turning to Figure 2, the hexagonal base portion 24 of the plunger 12 and the splined portion 34 of the body 14 are more clearly visible.

The hexagonal cross section of the base portion 24 enables the plunger to be inserted into the ring of a suitably sized ring spanner, or a suitably sized open spanner to be placed over the plunger, and the extender bar to be turned using the spanner. This is useful where there is insufficient space to use a ratchet tool to turn the extender bar, or where it is desired to use a spanner that is longer than the ratchet tool to start a jammed nut or bolt.

Where a ring spanner is so used, the cylindrical intermediate portion 26 enables the ring spanner to be slid off the hexagonal base portion 24 and onto the intermediate portion 26, which can turn freely inside the ring of the ring spanner.

In this way the ring spanner can be disengaged from the base portion of the plunger once the nut or bolt is started, and the extender bar turned using the ratchet tool or one's fingers.

Where it is desired to turn the extender bar using one's fingers, the splined portion 34 of the body provides a purchase, which is valuable where the extender bar is used in oily or greasy conditions.

The generally hexagonal cavity of the body that accommodates and engages with the hexagonal base portion of the plunger has six parallel channels, one channel being formed at each apex of the hexagonal cavity.

The channels allow very slight rotation of the hexagonal base portion of the plunger relative to the hexagonal cavity in the body. This causes the body to transmit a torque from a ratchet tool to the base portion of the plunger predominantly through the flats of the base portion, rather than through its apices. This greatly reduces the shear stress on the apices of the base portion of the plunger, and enables the extender bar to be used to transmit greater torques than would otherwise be possible.

Turning to Figure 3, this shows the entire plunger 12 and, in particular, the notches 52 that are formed in each of the apices of the base portion 24 distal from the stud 28.

The notches 52 become visible to a user of the extender bar only when the plunger has been moved to its maximum recommended extension relative to the body, which is when approximately 4mm of the base portion of the plunger is engaged with the body. Turning the screw 16 anticlockwise after the notches 52 become visible will further extend the plunger until the plunger is driven free of the body, which enables component parts of the extender bar to be cleaned and oiled.

The extendible coupling devices of Figures 4,5 and 6 are also in the form of extender bars denoted, respectively, by reference numerals 100,200 and 300. Where the devices of Figures 4 to 6 have parts in common with the device of Figures 1 to 3, these are denoted by similar reference numerals.

The extender bar 100 of Figure 4 comprises a plunger indicated generally by reference numeral 112, a body indicated generally by reference numeral 114 and an adjustment mechanism in the form of a key indicated generally by reference numeral 116.

The plunger 112 is of generally similar construction to that of Figures 1 to 3. However, the plunger 112 is formed with a central axial hole 130 that is generally circular but from diametrically opposed walls of which two series of teeth 154 project radially inwards, each series of teeth being disposed axially along the wall. The hole 130 continues for the entire length of a base portion 124 of the plunger 112.

The body 114 is of generally similar construction to that of Figures 1 to 3, having a wide portion 132 and a narrow portion 136, the wide portion 132 defining a generally hexagonal cavity 140 and the narrow portion 136 defining a socket 138. The socket 138 and cavity 140 are separated by a partition 142 with a central hole sized to receive the shaft 148 of the key 116.

The key 116 is a hardened steel shaft 148 from one end of which two sets of three teeth 156 project radially outwards, the sets being diametrically opposed to one another. The other end of the shaft 148 is formed into a screw head 146. The key is disposed in the body such that the screw head 146 of the key is accommodated in the socket 138 and the remainder of the shaft 148 and teeth 156 project through the hole in the partition 142 into the cavity 140.

The shaft 148 has a threaded portion adjacent to the screw head 146 onto which a lock nut 152 is tightened against a washer 150 that abuts the partition 142 to maintain the screw head 146 in abutment with a washer 144 that abuts the opposite side of the partition 142.

The screw head 146 enables the key to be rotated relative to the body by means of a screwdriver.

As shown in Figure 4, the teeth 156 of the key are engaged with the teeth 154 of the plunger, which prevents movement of the plunger into or out of the body. Rotation of the key relative to the body by a quarter turn disengages the teeth from one another so that the plunger can be moved into or out of the body.

Further rotation of the key relative to the body by a quarter turn re-engages the teeth with one another, provided that the teeth are suitably aligned with one another. The teeth are tapered so that if the teeth are not fully aligned when the key is further rotated by the quarter turn, the tapered forms of the teeth force the plunger slightly into or out of the body until the teeth are aligned, from which position the plunger is prevented from moving relative to the body.

The extender bar 200 of Figure 5 comprises a plunger indicated generally by reference numeral 212, a body indicated generally by reference numeral 214 and an adjustment mechanism in the form of a notched pin indicated generally by reference numeral 248 and ball bearings 256.

The plunger 212 is formed with a central axial hole 230 that is generally circular but the walls of which are formed by a series of annular recesses 254, the series of annular recesses being disposed axially along the walls. The hole 230 continues for the entire length of the base portion 224 of the plunger 212.

The body 214 is of generally similar construction to that of Figure 4, except that a cylindrical tube 258 projects from the centre of the partition 242 along the centre of the hexagonal cavity 240 for almost the entire length of the cavity. The tube 258 has four holes in its wall a small distance short of the free end of the tube. The four holes are spaced equidistantly around the circumference of the tube and at the same distance from the free end of the tube. The holes are sized to receive a ball bearing 256.

The notched pin 248 is a hardened steel shaft that is widened at one end to form a button 246 and that has an annular notch 260 a short distance from the other end. The pin 248 is disposed in the body such that the button 246 is accommodated in the socket 238 and the remainder of the pin 248 projects through the hole in the partition 242 into the cavity 240.

A helical compression spring 262 located around the pin 248 between the partition 242 and the button 246 urges the pin out of the socket 238 against a stop (not shown).

The external diameter of the pin 248 is such as to provide a sliding fit inside the tube 258.

With the pin urged against the stop, the notch 260 of the pin is displaced a small distance from the holes in the tube 258 that contain the ball bearings 256. The cylindrical surface of the pin therefore bears against the ball bearings forcing them outwards into one of the annular recesses 254. The ball bearings 256 are partially contained by the holes in the tube 258 and an annular recess 254, which prevents movement of the plunger relative to the body, as shown in Figure 5.

If the button 246 is pushed into the socket 238 so as to compress the spring 262, the notch 260 in the pin 248 is aligned with the holes containing the ball bearings 256 allowing the ball bearings to be received into the notch. The plunger can then be moved relative to the body because the ball bearings will be forced out of the annular recess 254 until they are contained in the holes in the tube 258 and the notch 260 in the pin. When the button 246 is released, the notch is displaced from the holes containing the ball bearings, forcing the ball bearings out of the notch and into whichever annular recess 254 is adjacent to the holes in the tube, which prevents further movement of the plunger relative to the body.

The extender bar 300 of Figure 6 comprises a plunger indicated generally by reference numeral 312, a body indicated generally by reference numeral 314 and an adjustment mechanism in the form of an oil-damped telescopic ram indicated generally by reference numeral 316.

The plunger 312 is formed with a circular central axial hole in the wall of which is formed an annular recess a short distance from a blind end of the hole. The hole continues for one third of the length of the base portion 324 of the plunger 312.

The body 314 is of generally similar construction to that of Figure 5, except that the cylindrical tube 358 projects from the centre of the partition 342 along the centre of the hexagonal cavity 340 for only half of the length of the cavity. The tube 358 is closed at its free end except for an axial hole in the centre of the end surface of the tube. A small lip 370 projects radially outwards from the free end of the external cylindrical surface of the tube 358. The tube 358 and the partition 342 from which it projects therefore define a first cylindrical cavity 372.

A further cylindrical tube 374 fits over the free end of the cylindrical tube 358. The tube 374 is closed at its free end and has an internal diameter that forms a sliding fit with the circumferential external surface of the lip 370. A small lip 376 projects radially inwards from the open end of the internal cylindrical surface of the tube 374. The lip 376 has an internal diameter that forms a sliding fit with the external cylindrical surface of the tube 358. The tube 374 and the closed free end of the tube 358 define a second cylindrical cavity 378. An o-ring seal 380 encircles the tube 358 between the lips 370 and 376 to prevent oil escaping from the second cylindrical cavity 378 between the external surface of the tube 358 and the internal surface of the tube 374.

The closed end of the tube 374 is provided with an annular recess in its cylindrical outer surface a short distance from the end of the tube. The tube 374 is attached to the plunger 312 by means of a circlip 382 that is partially contained in the annular recess in the outer surface of the tube and partially contained in the annular recess near to the blind end of the hole in the plunger.

A pin 348 is located in the body and passes through the hole in the end surface of the tube 358 and through the hole in the partition 342 that separates the hexagonal cavity 340 from the socket 338. The pin widens into buttons at its ends. One button 346 is accommodated in the socket 338 and the other button 384 is accommodated in the second cylindrical cavity 378. A helical compression spring 362 located around the pin 348 between the partition 342 and the button 346 urges the pin out of the socket 338 until the button 384 abuts an o-ring seal 386 that encircles the pin 348 between the end surface of the tube 358 and the button 384. The internal surface of the hole through the partition 342 is formed with an annular recess to accommodate a further o-ring seal 388, which encircles the pin 348 and prevents oil escaping from the first cylindrical cavity 372 between the internal surface of the hole in the partition 342 and the external surface of the pin 348.

As shown in Figure 6, with the button 384 abutting the seal 386, flow of oil between the cavities 378 and 372 is prevented and the plunger resists movement into and out of the body.

If the button 346 is pushed into the socket 338 so as to compress the spring 362, the button 384 is moved out of abutment with the seal 386 so that oil can flow between the cavities 372 and 378. With the button 346 depressed, the plunger can be drawn out of the body with associated flow of oil from the first cavity 372 to the second cavity 378, or pushed into the body with associated flow of oil from the second cavity 378 to the first cavity 372.

When the button 346 is released, the button 384 is forced into abutment with the seal 386, which prevents further flow of oil between the cavities. With the oil prevented from flowing between the cavities the plunger cannot be pushed into the body because this would involve compression of the oil in the second cavity 378. If the plunger is drawn from the body a vacuum will be formed in the second cavity 378, such that when the plunger is released it will return to its original position. The circlip 382 is chosen so that if it is attempted to draw the plunger from the body without the button 346 depressed to allow flow of oil between the cavities, the circlip will close and allow the plunger to be removed from the body before the telescopic ram can be damaged.

It will be apparent that the above description relates only to four embodiments of the invention, and that the invention encompasses other embodiments as defined by the claims set out hereafter.