An apparatus for operating on tissue, the apparatus comprising (a) a transducer assembly , wherein the transducer assembly is operable to convert electrical power into ultrasonic vibrations; and (b) a shaft assembly , wherein the shaft assembly comprises: (i) an ultrasonic waveguide , wherein the waveguide is configured to couple with the transducer assembly , (ii) a sheath , wherein the waveguide is disposed within the sheath , wherein the sheath is secured to the waveguide via a pin passed through aligned openings in sheath and waveguide to thereby couple sheath and waveguide such that rotation of sheath causes concurrent rotation of waveguide , wherein the opening in the waveguide is located at a location corresponding to a node associated with resonant ultrasonic vibrations, (iii) a shroud , wherein the sheath extends through the shroud , and (iv) a torque transfer assembly contained within the shroud , wherein the torque transfer assembly comprises an interior bore within which the sheath is rotatably disposed such that the torque transfer assembly is configured to transfer a predetermined range of torque from the shroud to the waveguide via the sheath to thereby couple the waveguide with the transducer assembly , wherein the torque transfer assembly is further configured to prevent transfer of torque from the shroud to the waveguide beyond an upper limit of the predetermined range. (a) a transducer assembly , wherein the transducer assembly is operable to convert electrical power into ultrasonic vibrations; and (b) a shaft assembly , wherein the shaft assembly comprises: (i) an ultrasonic waveguide , wherein the waveguide is configured to couple with the transducer assembly , (ii) a sheath , wherein the waveguide is disposed within the sheath , wherein the sheath is secured to the waveguide via a pin passed through aligned openings in sheath and waveguide to thereby couple sheath and waveguide such that rotation of sheath causes concurrent rotation of waveguide , wherein the opening in the waveguide is located at a location corresponding to a node associated with resonant ultrasonic vibrations, (iii) a shroud , wherein the sheath extends through the shroud , and (iv) a torque transfer assembly contained within the shroud , wherein the torque transfer assembly comprises an interior bore within which the sheath is rotatably disposed such that the torque transfer assembly is configured to transfer a predetermined range of torque from the shroud to the waveguide via the sheath to thereby couple the waveguide with the transducer assembly , wherein the torque transfer assembly is further configured to prevent transfer of torque from the shroud to the waveguide beyond an upper limit of the predetermined range. (i) an ultrasonic waveguide , wherein the waveguide is configured to couple with the transducer assembly , (ii) a sheath , wherein the waveguide is disposed within the sheath , wherein the sheath is secured to the waveguide via a pin passed through aligned openings in sheath and waveguide to thereby couple sheath and waveguide such that rotation of sheath causes concurrent rotation of waveguide , wherein the opening in the waveguide is located at a location corresponding to a node associated with resonant ultrasonic vibrations, (iii) a shroud , wherein the sheath extends through the shroud , and (iv) a torque transfer assembly contained within the shroud , wherein the torque transfer assembly comprises an interior bore within which the sheath is rotatably disposed such that the torque transfer assembly is configured to transfer a predetermined range of torque from the shroud to the waveguide via the sheath to thereby couple the waveguide with the transducer assembly , wherein the torque transfer assembly is further configured to prevent transfer of torque from the shroud to the waveguide beyond an upper limit of the predetermined range. <EOS>