Premium Material: The in-line coupler is made of high-quality plastic material, with high hardness, durable and safe. The plugs of telephone cord coupler are made of pure-copper, which ensures stable signal transmission and clear communication Feature: Compress all the spare space, accurate signal transmission, small and exquisite, compact and durable. Easy to install and no static or distortion of voices Main Function: It is used to connect and extend two existing telephone lines with R11 telephone head (6P4C, 6P2C crystal head) at both ends through telephone through box