a locking jaw assembly having a workpiece clamping top jaw securely interconnectable to a master jaw by a key locator and a lock bolt wherein the top jaw may be readily removed from the master jaw by simply loosening the lock bolt and another top jaw may be readily interconnected to the master jaw with repeatable precision by retightening the loosened lock bolt . the secure interconnection of the top jaw to the master jaw by the key locator and lock bolt is augmented by a lip portion of the master jaw received in a complementary shaped groove disposed on a flange of the top jaw wherein forces exerted by the workpiece on the top jaw tend to move the top jaw into closer contact with the master jaw and relieve tensile stresses on the key locator .