A cord coupler is a device that joins two different pieces of wire, cord, or cable together. Although the term usually refers to telephone cords, couplers can also be used with video, audio, power, and network cables. Couplers can even be used to join two different fabric cords or ropes.
Telephone cord coupler devices typically contain two female registered jack (RJ)-11s with each of their pins connected directly to the corresponding pin on the other jack. They offer a straight-through connection for the signal carried by the jack. Most people use these types of cord couplers to join two short telephone cords together to make one long cord.
Traditionally styled phones with separate handsets can also use a handset cord coupler. This coupler has a pair of small female handset jacks which look like an RJ-11 jack but are a bit smaller. These narrower jacks, referred to as "4P4C" jacks are identical to RJ-11 jacks but smaller and with only four conductors. Some handset couplers also include a swiveling attachment to prevent the attached handset cords from getting tangled.
In addition to telephone cords, cord couplers join many other types of cables together. Network administrators use couplers with RJ-45 jacks to turn short Ethernet® cables into long ones and can do the same with fiber optic cable couplers. Cable television installers frequently use F-couplers to join two cable television coaxial cables together. Manufacturers of lanyards and other products made of fabric cording or rope can also buy couplers to join two short pieces together into a long one.
Regardless of what application a cord coupler is serving, its convenience comes with a price. Two short cords coupled together will never be as strong as a single long cord. With electrical signals, the coupling leads to the risk of noise, interference, and signal loss. In a fabric cord, the coupling is a weak point and compromises the tensile strength of the entire cord. In either case, couplers can be an excellent way to turn two short cables into one long one, but the best solution, in settings where performance cannot be compromised, is to forgo use of a coupler and simply use a longer piece of cord.