Design Considerations The wrench had to grip 15mm and 22mm copper pipe without damage and be self gripping, I.e. no part of the wrench would need to be held for it to grip the pipe. To enable the wrench to grip without damage, a rubber drive belt was chosen as the gripping agent. A piece of part worn fan belt was utilised. To permit adjustment of the tension and to retain it an adjustment screw was used. Photograph 3 shows an overall view of the assembled wrench. The dimensions chosen were such that the body of the wrench fitted in the hand. The length of the body, in conjunction with the length of the screw, determines the adjustment range of the wrench .
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