(in Russian, shtutser). A union or a nipple is a pipe fitting that is used to attach piping or a pipe joint to various tanks or pipelines. A union is a sleeve, while a nipple is a short piece of tubing. One of the ends of a union or a nipple has an internal or external screw thread; the shape of the other end depends on the method used to connect the fitting to adjoining parts.
The term “nipple” is also applied to a short piece of tubing of small diameter (10–20 mm) that is used to draw off water or air or to tap a liquid from piping in order to measure the pressure of the fluid.