Coupling (piping)
In piping and plumbing, a coupling (or coupler) 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.