Abstract: An inexpensively manufactured discrete keying device for connector, plugs and sockets of standard types. Two or more mating grooves and finger members are coded by discretely spacing them circumferentially. The grooves are axial and are cut into the turnable captive internally threaded body shell member of one matable subassembly of the connector arrangement and the finger members are radially inwardly directed projections having matching circumferential spacing within the wall of a sleeve member associated with the other connector subassembly. Where a plurality of such connectors are adjacent to each other, mismating is prevented by separate finger and groove spacings for each corresponding connector assembly.