There are a variety of different types of Registered Jack connectors.
An RJ12 connector is a 6P6C (6 poles, 6 connected) data connector commonly used for telephone systems as well as data networks. RJ12 modular connectors are constructed from clear plastic and have 6 gold contacts. They feature a tab that helps secure the plug into place providing a secure connection between plug and socket or faceplate. RJ12 connectors can be used with solid or stranded wire.
What does an RJ12 connector do?
RJ12 connectors are used for connecting data and voice equipment to the local exchange network. These connectors are typically used to connect telephones to landlines.