There is disclosed a locking unit (100) for locking a pusher (128) to a sheath assembly (164). The locking unit (100) includes a longitudinal locking portion (102) and a radial locking portion (104). The longitudinal locking portion (102) includes a plurality of cantilevered fingers (110) provided with longitudinally extending teeth (112) on internal surfaces thereof. A nut (108) can be tightened in order to bias the cantilevered arms (110) towards a pusher (128) such that the teeth (112) indent the outer surface of the pusher (128) to produce a strong and stable locking connection thereto. The radial locking section (104) latches onto the assembly integral with the sheath (164) so as to provide a radial locking action as well as a longitudinal locking action. The locking unit (100) provides a strong and reliable locking action between the pusher (128) and the sheath assembly (164) and can be easily removed by a clinician or surgeon during the deployment process.