Pipe nipple is a length of straight pipe with male threads on both ends. It is one of the most popular category of pipe fittings.

It is a connector or a coupling threaded on both ends. Pipe nipples are used to allow plumbing to be connected to a water heater or other plumbing. They are used to fit straight end hose or pipe. A combination of pipe nipples are recommended for low-pressure discharge and suction service for various compatible liquids and not for compressible products like air, nitrogen or steam.

The length of the pipe nipple is usually specified by the overall length with threads. It may have a hexagonal section in the center for wrench to grasp (sometimes referred to as a “hex nipple”), or it may simply be made from a short piece of pipe (sometimes referred to as a “barrel nipple” or “pipe nipple”).