An ultrasonic surgical instrument includes a body, an ultrasonic transducer rotatably supported within the body and having a threaded distal end, a shaft extending from the body, a waveguide extending through the shaft and having a threaded proximal end configured to threadedly engage the threaded distal end to define a threaded coupling, and an end effector at a distal end of the shaft. An integrated torque wrench mechanism is arranged within the body and includes a first torque wrench member rotationally coupled with a proximal end of the transducer, and a second torque wrench member arranged proximally of the first torque wrench member. The torque wrench members are configured to selectively couple together and frictionally engage one another to facilitate application of a predetermined maximum torque to the threaded coupling. The torque wrench members are configured to automatically decouple upon application of the predetermined maximum torque to the threaded coupling.