Abstract: A system of keying of a panel mounted connector and a mating connector is provided where each of the connectors is of the type having forward and rearward thin walled metal shells clinched together about their flanged edges to retain a housing means therewithin, with the forward and rearward shells having adjacent apertured lateral flanges enabling mounting of either one of the connectors to a panel at an I/O port of an electronic apparatus by screw means. The keying system includes a pair of key members each securable to the front of the forward shell at a respective lateral flange, by the corresponding screw means extending through the apertures of the rearward and forward shell flanges and threaded into a threaded key member aperture. The key members may have octagonal cross-sections and are seated within correspondingly octagonally shaped flange apertures of the forward shell only, held against the front surface of the rearward shell.