We get quite a few customers who are confused over what plug they have in their hands or what plug they require! Plugs have Poles & Contacts, eg, 6P4C means the plug has 6 Poles (or slots as you see them) but only FOUR are in use and have gold Contacts!
BT431A. This is the most common plug & is used in the UK (& various foreign countries!) to plug a telephone into the wall socket. With the plug facing away the latch is on the right hand side. Most commonly white in colour. 6P4C 4 way connector.
BT631A. Exactly the same as the 431A above in terms of size but this plug is a 6 way as opposed to 4 way. Most commonly used in office phone systems (PBX systems), the extra pins are usually used for what are called feature phones. 6P6C 6 way connector.
RJ45. These are commonly used in network (Ethernet) environments, various classes are available such as CAT5e & CAT6. All versions are physically the same size and feature 8 pins, approx. 11mm wide. 8P8C 8 way connector.
RJ11. These are commonly used to connect routers, modems & telephones to the telephone line. They are a 4 way plug, approx. 9mm wide. An RJ11 plug will plug into an RJ12 & RJ45 socket! In many foreign countries this plug is used in place of the BT style plug/socket. 6P4C 4 way connector.
RJ12. These are physically the same size as the RJ11 above but feature 6 contacts rather than 4. Commonly used to connect telephones to PBX systems (in conjunction with the BT631A plugs above). They are approx. 9mm wide. An RJ12 plug will plug into an RJ11 & RJ45 socket! 6P6C 6 way connector.
RJ10. These are the smallest plugs in the RJ series & are also known as RJ9 & RJ22 plugs! They are a 4 way plug but smaller than RJ11. Commonly used to connect handsets & headsets to telephone base stations. They are approx. 7mm wide & will NOT plug into any other RJ series socket! 4P4C 4 way connector.