Threaded Nipple
It is a short stub of pipe which has a male pipe thread at each end and a plain pipe on the other. It used for welding connection to a vessel or a tube, and to a threaded fitting or valve on the other side.
Description
When it comes to plumbing and piping, a nipple is a fitting that is a short piece of pipe. A nipple is usually provided with a male pipe thread (MPT) connection at each end of the fitting, which are used to make a watertight seal when connecting piping to threaded fittings, valves or equipment.