This invention relates to fissure cam devices used in rock climbing and known variously as Friends and Quadcams, as well as by other names.

Such devices comprise opposed cams mounted for rotation on an axle and resiliently biased into an open position. The axle is carried on a support member along which moves a trigger. Pulling on the trigger closes the cams so they can be inserted into a rock fissure or cavity, and releasing the trigger, when the cams have been positioned, allows them to open under this bias into contact with the sides ofthe fissure or cavity. Tension on the support member, to which the climber's rope is attached, tends to open the cams further, which applies them with greater force against the rock, reinforcing the grip of the device. Such devices are capable of supporting the climber and even of breaking a fall.

In devices such as Friends which have two pairs of opposed cams on the same axle, one pair either side ofthe support member, if the support member is moved. during rope manoeuvres, from side to side, the device can move deeper into a fissure and may move so far in that the cam surfaces fail to maintain effective contact with the fissure walls and in the event ofa fall, the forces may act in such a way as to over-rotate the cams which then fail to hold the fall.

In one design of device the axles for one pair of cams operate in slots in. and act as stops for, the other pair of cams, and this problem of over-rotation does not arise. But such two-axle devices are heavy for their size, and equipment weight is at a premium in rock-climbing, and single-axis devices are to be preferred on that ground and for other reasons.

In one very recently developed single-axis device, cams of each pair are machined from solid casting to form abutments preventing over-rotation, but this is expensive and is only available on smaller devices suitable for narrow fissures.

Another problem with all such devices lies in the connection ofthe trigger to the cams by means of control wires. The wires run from each cam, between the pairs of cams, down to the trigger and in larger devices, unless the trigger is so wide as to be inconvenient to operate, the wires bend around the inboard cams and can catch, creating difficulties in use.

For stability in cracks it is desirable that the axle should be at least as long as the distance between opposed cam faces at half-opening. In small devices, however, because ofthe arrangement ofthe control wires, the axle is necessarily far too long - over twice what it needs to be - and this militates against the use of the devices, in more restricted access cracks.

These problems are solved or their effects reduced in devices according to the invention.

The invention comprises, in one aspect, a fissure cam device comprising a single axle arrangement of co-operating cams urgeable against an opening bias by a trigger movable along a support member attached to the axle into a closed position for insertion into a fissure the cams having fissure wall-engaging edges maintained in operative contact with the fissure walls by the opening bias such contact being reinforced by any tension on the support member, at least one cam of a co-operating pair of cams having a stud set into it and projecting into the path of the other cam about the axle to define a limit of relative rotation and prevent over-rotation.

Each of said co-operating pair of cams may have a stud projecting into the path of the stud on the other of said pair.

The trigger may be attached to the cams by wires projecting from the cams towards the support member. The cam further from the support member may have a wire-attaching stud projecting axle-parallel towards the support member into the path of the cam member nearer the support member. This wire-attaching stud may itself form an or the abutment against over-rotation.

The invention also comprises, in another aspect, a fissure cam device comprising a single axle arrangement of cooperating cams urgeable against an opening bias by a trigger movable along a support member attached to the axle into a closed position for insertion into a fissure, the cams having fissure wall-engaging edges maintained in operative contact with the fissure walls at least one cam of a cooperating pair of cams having a projection forming a control wire attachment to said cam whereby the wire thereto attached operates between the innermost cams.

Embodiments of fissure cam devices according to the invention will now be described with reference to the accompanying drawings in which:

Figure 1 is an edge-on elevation of a prior art device ;

Figure 2 is a face-on elevation of one embodiment ofa device according to the invention ; and

Figure 3 is an edge-on elevation of a second embodiment of a device accordinε to the invention.

The drawings illustrate fissure cam devices comprising a single axle (1 1) arrangement of co-operating cams 12 urgeable against an opening bias by a trigger 13 movable along a support member 14 attached to the axle 1 1. The opening bias is applied in the direction of Arrows A - see Figure 2, the face cam elevations ofthe devices of Figures 1 and 3 being similar, save for the details of features ofthe invention - by torsion springs 15 surrounding the axle 11 and hooked over pins 16.

The cams 12 have fissure wall-engaging edges 17 maintained in operative contact with the fissure walls 18 by the opening bias - see in this regard the silhouette in the lower part of Figure 2. Such contact is reinforced by any tension on the support member, and may result from a fall through the rock-climber's rope attached through an eye 14A ofthe support member 14.

Repeated movement of the device in the fissure can result in the cams "walking" up the fissure to a position - as shown in the upper part of Figure 2 where the fissure is wider than the maximum width ofthe device with the cams 12 fully opened out. Conventional single axis devices, as shown in Figure 2, can then over-rotate and fall catastrophically out ofthe fissure.

As shown in Figure 2, however, each ofthe cams 12 has a stud 19 set into it and projecting into the path of the other stud 19 - and hence the cam - about the axle 1 1 to define a limit of relative rotation and prevent over-rotation. In Figure 2, the studs 19 are in contact and further rotation ofthe cams 12 about the axle 1 1 in the direction of Arrows A is not possible.

As will also be seen from Figure 1, the trigger 13 is conventionally attached to the cams 12 by wires 21 which run from each cam 12, between the pairs of cams 12 on either side ofthe support member 14, and they have to bend around the edges ofthe cams 12, where they are likely to snag. For small devices it will be appreciated that to

accommodate the wires 21 in the space between each co-operating pair of cams 12 requires a disproportionably wide spacing between the cams 12.

Figure 3 illustrates how by putting a stud 31 in each ofthe outermost cams 12 to carry its wire 21 to within the spacing between the two innermost cams 12, and bringing the wires of the innermost cam 12 out on their inner, rather than their outer sides, all four wires 21 can be kept out ofthe space between the right and left hand co¬ operating pairs of cams 12 with no risk of snagging on the edges of same.

If, moreover, the stud 31 is of sufficiently sturdy design, it can serve as well as the or a stud that keeps the device from over-rotating - see the broken line position at 31A on Figure 2 where the studs 31 abut the edges of the cams 12 in the opened-out position. There is, of course, with this arrangement, no need also to have the studs 19.