Abstract: A chuck is disclosed for gripping an annular workpiece by jaws clamping against the inside wall of the workpiece. The jaws extend axially of the chuck and are rocked between clamping and release positions by levers which contact the radially outer face of the rearward end of the jaws as a result of pivoting about a point adjacent the radial outer periphery of the chuck body. The levers are moved by an axially movable actuator at the axial center of the chuck. The arrangement provides a mechanical advantage such that the chuck in closed position is substantially self locking.