Abstract: A shell sleeve serves for the reception of a bearing socket. The shell sleeve possesses the shape of a body of revolution or rotation which tapers or narrows towards a pole region. This body of revolution carries at its outer surface a self-tapping thread. To facilitate threading-in of the shell sleeve into the bone substance or material and to preclude, during such threading-in operation, the application of forces which would cause any pressure and splintering action upon the bone substance or material, the thread comprises a flat thread. This flat thread has flanks dispositioned at essentially right angles to the lengthwise axis of the body of revolution and the spacing from thread flight to thread flight is constant. The portions of the thread flights which follow a related cutter or cutting surface thereof are undercut or machined back.