A slaving and blocking device for transmitting a torque from a driving part to a driven part and for stopping the driven part at a torque engaging the driven part has a slaving element fixable on the driving part and having slaving claws offset from one another in a circumferential direction, a roller...http://www.google.com/patents/US7287602?utm_source=gb-gplus-sharePatent US7287602 - Spindle lock for rotary power tool
