In pipe construction, the term ‘fittings’ refers to connecting elements or other accessories. They are available in dozens of different varieties. As a rule, all of these parts are used for connecting one or more pipes or for installing fittings or components used for metering. The only exception is the stopper. This serves as a closure for a pipe. Apart from this, there are connectors as well as and screw connection and angle pieces. The term ‘nipple’ is used for simple connecting elements with external threads. Examples include double nipples, reduction nipples and pipe nipples. The term ‘piece’ generally refers to connections with internal threads or bonded socket joints such as tees, crosspieces and reducers. Reducers, however, are equipped with an internal thread on one side only. Angles and screw connections also come under the category of ‘pieces’. The complete range of pipe fittings is, of course, available not only with threaded connections but also with bonded socket joints. In such cases, the plastic fittings are glued to the pipes or fittings. Other connecting elements, in addition to threaded fittings or bonded fittings, include flanges.