Ultrasonic surgical instrument having a handle assembly, a waveguide extending distally from handle assembly, an end-effector at distal end of the waveguide, and a clamp assembly removably mounted to the handle assembly. The clamp assembly includes a pivotally mounted clamp arm for pivotal movement with respect to the end effector, and is removably mounted to the handle assembly by axially aligned first and second bayonet mounts. Each of the bayonet mounts includes a female bayonet coupling having at least one bayonet slot configured to matingly receive a bayonet mounting pin of a male bayonet coupling, wherein the bayonet slots extend circumferentially about the longitudinal axis of the waveguide. A method of removing the clamp assembly of the ultrasonic surgical instrument is also provided, as well as an ultrasonic surgical shears instrument and a clamp assembly.