Registered Jack (RJ, "ar-jay" is read in English) is a standardized physical network interface that includes a description of the design of both parts of the connector ("plug" and "socket") and their switching schemes. Used to connect telecommunication equipment. There are several types of RJ series connectors: 4P4C, RJ-11 6P2C and 6P4C, RJ-12 6P6C, RJ-45 8P8C, 10P10C.
The 4P4C connector, another name for RJ-9, is mainly used to connect handsets to telephones, these are the smallest connectors from the RJ series, they have four lamellas and four contacts.
RJ-11 connectors, these connectors are used to connect telephone cables and connect landline telephones, RJ-11 plugs are of two types: two-pin, labeled 6P2C and four-pin labeled 6P4C.
RJ-12 connectors, also known as RJ-25, have six pins, labeled 6P6C, and are mainly used for connecting proprietary telephones with a six-pin connector.
RJ-45 connectors, have eight pins, labeled 8P8C, are designed to connect telecommunications equipment: computers, sockets, network switches, patch panels. These connectors are subdivided into several types, depending on the cable used.
10P10C connectors, also called RJ-50, have ten pins and are used to control uninterruptible power supplies, barcode scanners, and medical equipment.
RJ-45 and 10P10C connectors have different color-coded rubber caps to prevent the cable from kinking and damaging it further.