A surgical instrument is separable into a transducer unit and a lower body portion. The lower body portion includes a waveguide and a casing. The transducer unit includes a transducer and a geared mechanism operable to couple the transducer to the waveguide. In some versions the geared mechanism includes bevel gears coupled to a rack and pinion such that linear motion may be used to rotatably couple a transducer to a waveguide. The rack gear may further include a handle extending out of the transducer unit casing to be actuatable by a user. The rack gear may also be flexible or rigid. In other versions, the bevel gears may be coupled to a threaded shaft that is operable to translate the transducer into the waveguide to form an interference fit. The transducer unit may also include a slide lock mechanism to couple to the casing of the lower body portion.