RJ13 Jack
Within the RJ (Registered Jack) standard , the RJ13 is the 6P4C version of the wall- and baseboard-mounted telephone jacks installed in residences. Compare RJ11 (6P2C), RJ12 (6P6C), RJ13 (6P4C), RJ18 (6P6C) and RJ25 (6P6C). The RJ13 jack is similar but not compatible with the British Telecom 431A/631A telephone sockets.