An RJ-45 standard modular plug receptacle is defined by walls including a wall defining a plurality of contact wire positions including a pair of outermost contact wire positions. A pair of stops project into the receptacle from a surface of the wall, the stops being in longitudinal alignment with the outermost contact wire positions. An RJ-45 plug is thereby fully insertable in the receptacle with the stops entering the outermost contact pin grooves on the plug during insertion. However, full insertion of an RJ-11 plug is prevented by said stops which engage front faces on the RJ-11 plug flanking the contact pin array of the RJ-11 plug.