According to the website Pipe & Tube Fittings, fittings for pipes are available in metric and standard measurement sizes. Consumers can purchase metric pipe fittings in sizes ranging from 10 mm all the way to 1,000 mm in diameter. Standard pipe fittings are available in sizes ranging from 1/8 inch up to 36 inches in diameter.
Different fittings are shaped and sized differently to serve different functions. Couplings, adapters, and caps are engineered to extend or terminate pipe runs. Elbows change direction of flow through a piping system. Tees and crosses connect a number of pipes together. Reducers and bushings are used to change the size of pipe runs.
Steel, aluminum, brass, cast iron, polyvinyl chloride (PVC), and copper are all materials used to fabricate pipes and pipe fittings. Some types of fittings are bulkier than others. For example, PVC and brass pipes can be quite substantial in size, while copper fittings can be as slender as the pipes they connect. Copper fittings are constructed in this way because they are soldered, not screwed, into the pipes they connect. As a result, copper fittings can be placed in spaces that are too restricting for other types of fittings.