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 plug. This serves as a closure for a pipe. Apart from this, there are nipples as well as unions and elbows. 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 female threads such as tees, crosses and reducing bushes. Reducing bushes are equipped with an female thread on one side only. Elbows and unions also come under the category of ‘pieces’.