Nipple

In the plumbing and piping trade, a nipple is a fitting that consists of a short piece of pipe that is usually provided with a male pipe thread at each end, for connecting to two other plumbing fittings. The length of the nipple is usually specified by the overall length including the threads. It may have a hex section in the center for wrench to grasp.

A close nipple has no unthreaded area; when screwed tightly between two female fittings, very little of the nipple remains exposed. A close nipple can only be unscrewed by gripping one threaded end with a pipe wrench which will damage the threads and necessitate replacing the nipple, or by using a specialty tool known as a nipple wrench (or known as an internal pipe wrench) which grips the inside of the pipe, leaving the threads undamaged. When the ends are of two different sizes it is called a reducer or unequal nipple. A barrel nipple or a pipe nipple is one which is usually made from pipe and is threaded only at both ends.