A clutch assembly for limiting a torque output of the power tool. The clutch assembly includes an annular rotatable clutch member, which is coupled to the ring gear of a planetary gearset in a transmission, and an engagement assembly. The clutch member has a clutch face with a predetermined clutch profile....http://www.google.com/patents/US6857983?utm_source=gb-gplus-sharePatent US6857983 - First stage clutch
