Coupling (piping)

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A Coupling (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 welded (steel), brazed or soldered (copper, brass etc.) together.

Alternatively it is a short length of pipe with two female NPT (National pipe thread)s (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 are different, for example one BSP threaded and one NP 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 are of a different size it is called a reducing coupling.