a fitting that connects pipes of different diameters, genders, or threads (see § Coupling below).
Any material permitted by the plumbing, health, or building code (as applicable) may be used, but it must be compatible with the other materials in the system, the fluids being transported, and the temperature and pressure inside (and outside) the system. The bodies of fittings for pipe and tubing are most often the same base material as the pipe or tubing connected: copper, steel, PVC, CPVC, or ABS. Non-metallic (includes acrylonitrile butadiene styrene (ABS), fibre-reinforced plastic (FRP), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), high-density polyethylene (HDPE), and toughened glass polybutylene has also been used, but is now banned in North America because of poor reliability).Non-ferrous metals (includes copper, inconel, incoloy, and cupronickel).Chrome-molybdenum (alloy) steel (generally used for high-temperature service).Materials used for manufacturing pipes include: The material with which a pipe is manufactured is often the basis for choosing a pipe. 6.9 Double sanitary tee (sanitary cross).6 Drain-waste-vent (DWV) and related fittings.