A coupling (or coupler) (used in piping or plumbing) is a very short length of pipe or tube, with a socket at one or both ends that allows two pipes or tubes to be joined, welded (steel), brazed or soldered (copper, brass etc.) together.
Alternatively it is a short length of pipe with two female National pipe threads (NPT) (in North American terms, a coupler is a double female while a nipple is double male) or two male or female British standard pipe threads.
If the two ends of a coupling are different (e.g. one BSP threaded and one NPT threaded), then it is usually referred to as an adapter. Another variation is one plain socket and one threaded socket. Yet another variation would be 3/4" NPT to 1/2" NPT.
When the two ends use the same connection method but are of a different size, the terms reducing coupling or reducer are used.
Grooved Pipe Couplings
Grooved couplings, offered by companies such as Victaulic, is up to three times faster to install than welding, easier and more reliable than threading or flanging, resulting in lowest total installed cost.
The grooved couplings system is designed for roll grooved or cut grooved standard pipe or roll grooved light wall pipe. Grooved couplings is a clean system whereby there is no pipe dope or welding slag to contaminate pipes. Each joint is a union and the removal of two couplings permits removal of pipe section for cleaning or servicing. Grooved couplings proven joint reliability. Full circumferential engagement of housing into groove provides end pull strength.
- ASME B1.20.7 Hose Coupling Screw Threads, Inch. (Quote: The normal sequence of connections, in relation to the direction of flow, is from an externally threaded nipple into an internally threaded coupling)