Shielded and keyed electrical connector assembly

Electrical connector assembly (2) comprises a plug (4) and a receptacle (6). A keying system (78,84) is provided which permits insertion of the plug (4) into the opening (52) of the receptacle (6) but which precludes insertion of a similar, but more narrow, plug (4) into the opening (52). The keying system (78,84) is advantageous when a series or family of connector assemblies (2) are produced with the different assemblies of the family being generally similar but having increasing numbers of terminals (62) and therefore increasing width. The plug (4) and receptacle (6) are provided with sheet metal shielding enclosures (98, 100), the plug shield (98) overlapping forward portions and extending to the rear of the plug, the forward portions having an unshielded section, the receptacle shield (100) being on the mating end and extending into the plug-receiving opening (52). The keyway on the plug being in the unshielded section and the key in the receptacle extending into the plug receiving opening (52) and spaced from the receptacle shield (100).