RJ11 telephone jack
Telephone RJ11 plug. Ref. SIM10040.10 of TDTprofesional.
This type of connector is the most widely used in telephone systems. It is of compact dimensions and has four 4-way contacts to support two cables. Generally they tend to use only the two central threads to a single line or twisted pair. Only four wires only for special telephone devices that use double line or two telephone pairs are used