A mechanical coupling between a straight pipe end and a socket fitting comprises a seal ring and a locking ring disposed within the interior of the socket. The locking ring has a generally frustoconical shape with a plurality of corrugations extending circumferentially thereabout, the corrugations presenting inner edge portions engaging the outer annular surface of the pipe end and outer edge portions engaging the interior annular surface of the socket for opposing withdrawal of the pipe end axially outwardly from the socket. In an advantageous embodiment, the locking ring is assembled with a support disk to optimally orient the locking ring with respect to the fitting and the pipe end.