Abstract: Novel locking means for coupling shafts together is disclosed in which the shafts are threaded together thus axially and radially locating the first and second shafts, and are locked by means of a knurled portion encircling a first one of said shafts interacting with an internally knurled key having a peripheral shape corresponding to a removed portion of a second shaft whereby relative rotation of the shafts is provided. In a preferred embodiment, one of said shafts comprises a tubular shaft formed integrally with an impeller of a pump which may be formed of fiberglass so as to be corrosion resistant. A collar may be provided to simultaneously lock the key to the two shafts.