Pipe fittings are usually classified according to the way they are used

Pipe fittings are essential for all systems that make use of plumbing pipes or supply water into a building. The fittings are often referred to as adapters because they are used to convert one type of pipe into another. There are basically two types of pipe fittings: the closed pipe fittings and open pipe fittings. A fitting or adapter is typically used in pipe networks to connect straight lengths of pipe or tube to various shapes or sizes, to adjust to different diameters, and also for other purposes like regulating the flow of liquid or gas. Pipe fittings are classified according to the ends they will cover, their internal diameter, threading pattern, and internal structures like enamel, steel, or bronze. Other materials that compose pipe fittings include materials like reinforcing thermoset polyethylene, synthetic rubber, polyvinyl chloride, epoxy, nylon, acrylic, and polycarbonate.

Closed pipe fittings are used in construction projects where there are no direct connections to the outside world and are enclosed inside steel or molded bodies. These may have different outer diameters, including small ends for connecting pipe fittings to thinner ones. The inner diameter, also called the stem diameter, refers to the pipe's interior diameter; the outer diameter refers to the diameter of the pipe's outer threads.

To repair, maintain, or install pipe fittings, you should have basic tools like an adjustable wrench, a pair of plumbing knives, a ratchet wrench, a pair of rubber or plastic pliers, an adjustable spanner, a measuring tape, a cable cutter, a pipe flashing, a caulking gun, a seal and bender, a cutting tool, and some filler material like cement, sand, or cement dust. Depending on the system you're working on, there are different tools and products available depending on the pipe size and construction. Pipe fittings are usually classified according to the way they are used, such as single-ended or double-ended, which depends on how they are fastened. Other classifications include closed or open, through or close, round or flat, internally or externally, man-made or natural, and self-adjusting or gravity fed.