Abstract: A clamp for releasably gripping a workpiece includes a base member, a first jaw portion attached to the base member and having a first gripping portion and a second jaw member pivotally coupled to the base member at a pivot location, and having a second gripping portion. The second jaw is pivotable about the pivot location between an open, retracted position where the first and second gripping portions are spaced apart and a closed, gripping portion where the first and second gripping portions engage the workpiece and apply a gripping force to hold the workpiece. An actuator selectively retracts the second jaw member from the gripping position into the retracted position by application of a retracting force. A mechanism which may include a cam or an over-center linkage releasably holds the second jaw member in the retracted position independently of the retracting force.