A surgical apparatus comprises a transducer assembly and a shaft assembly. The transducer assembly is operable to convert electrical power into ultrasonic vibrations. The shaft assembly comprises an ultrasonic waveguide, a sheath, a shroud, and a torque transfer assembly. The waveguide is configured to couple with the transducer assembly. The waveguide is disposed within the sheath. The sheath extends through the shroud. The torque transfer assembly is contained within the shroud. The torque transfer assembly is configured to transfer a predetermined range of torque from the shroud to the waveguide to thereby couple the waveguide with the transducer assembly. 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.