 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 of different standards or joining methods, the coupling is called an adapter.Examples of adapters include one end BSP threaded with the other NPT threaded, and one end threaded with the other a plain socket for brazing.