Abstract: A pair of work engaging jaws of a clamp device are interconnected by linkages forming part of a manually operable force multiplying mechanism. A movable work engaging element mounted by one of the jaws, is actuated by a grip lever from a retracted position into engagement with a workpiece. An over-center linkage transmits the actuating force against the resistance of a spring to prevent return of the grip lever from its actuated position. A release lever is actuated to cam the grip lever and retract the work engaging element.