Abstract: An improved chuck for opening and closing a split collet into which a work piece is inserted. The collet is inserted into a central bore in the chuck housing and a threaded end of the collet is threaded into a rotatable annular member located in a counterbore in the rear of the chuck housing. The rotatable annular member has forwardly directed cam surfaces which cooperate with rearwardly directed cam surfaces in the chuck housing. A recess provided in the radially outer surface of the annular member is aligned with a radial bore in the rear of the chuck housing. A cylindrical key rotatable within the radial bore has an eccentric shaft protuding into the recess in the outer surface of the annular member. Turning the key within the radial bore moves the eccentric shaft into contact with a wall of the recess and rotationally biases the annular member.