Abstract: An apparatus for gripping the interior surface of an annular opening in a workpiece includes a baseplate and a set of elements circularly arranged and coaxial with a shaft or stud extending through and perpendicular to the baseplate. The elements are circumferentially spaced apart and are slidable radially of the shaft.Each element has a pair of aligned curved slots opening respectively to the opposite circumferential ends thereof. Biasing springs are secured to the baseplate and positioned thereon to extend from a slot in one element to the adjacent slot in the adjacent element. These biasing springs bear against the side surfaces of adjacent slots for biasing the elements radially inwardly to a contracted position. An actuating member which is in the shape of a camming disc, is movable relative to the baseplate and cooperates with the elements to move them radially outwardly so that they engage and grip the interior surface of the opening in the workpiece.