A modular prosthesis is provided having a first and second prosthesis component and a locking nut. The first prosthesis component is configured to include a mating surface and a threaded shaft extending from the mating surface. The locking nut is formed to include a distal end having a shaped surface. The second prosthesis component is configured to include a mating surface, a nut-receiving cavity and a bore. The mating surface of the second prosthesis component is configured to mate with the mating surface of the first prosthesis component. The nut-receiving cavity is configured to receive the locking nut therein and to have a shaped bottom wall configured to engage the shaped surface of the locking nut. The bore communicates with the nut-receiving cavity through the shaped bottom wall and the mating surface and is sized to receive the threaded shaft therethrough. The threaded shaft, locking nut, bore and cavity are configured so that when the threaded shaft of the first prosthesis extends through the bore and the locking nut is received in the nut-receiving cavity and tightened onto the threaded shaft, the distal end of the locking nut is urged into engagement in multiple locations with the bottom wall of the cavity and the mating surfaces of the first and second components are urged into engagement.