Connection socket for trailers

The trailer socket (1) has a socket housing (2) and a contact carrier insert (3) received in the socket housing. The contact carrier insert has a receiving channel (6) for receiving electrical plug contacts provided with electrical connection lines. The receiving channel has an inner side circular projection. The socket housing and the contact carrier insert are integrally formed as an injection molded part from plastic. The socket housing and the contact carrier insert are connected with each other by a ring part. An independent claim is also included for a connecting system with rest pins.