A prosthetic joint for use in replacing the ball end of a biological joint, the replacement including a spherical head for insertion into a natural socket, an insert in the head and locked therein by an inwardly projecting ring in the head and a groove in the insert, a ball shaped member seated in the insert and having a neck and a stem for mounting the joint on the end of the biological member on which the ball is being replaced and a ring having a downwardly and inwardly sloping outer wall seating in a recess in the plastic insert and locking the ball shaped member in the insert.