Threaded fittings are probably the oldest mechanical method of joining pipes, hoses and other pneumatic devices. Pneumatic thread fittings have tighter seals and a lower pressure rating than hydraulic fittings and are used extensively in factories and other industries that require compressed air such as garages. Originally made solely of metal, modern threaded fittings can also be supplied in heavy duty non-toxic polymers that are more resistant to corrosion or fatigue, although more subject to heat expansion. Common types of material include nickel plated brass, stainless steel, plastic and polymer. Stainless steel fittings and advanced polymers are used in applications that require a high standard of hygiene such as the food and beverage industry. They come in a wide variety of dimensions, including the diameter, number of threads per inch or centimetre, and the normal engagement length.
Threaded fittings are commonly used in pneumatic control systems for connecting lengths of tubing, pipes and hoses in a pressurised system. Threaded fittings are found on a variety of hose and pipe connections, including blanking plugs, adapters, sleeves, reductions, nipple fittings and ring pieces, tees, hexagons, elbows, crosses and sockets. Fittings can be threaded with male or female connections and either a sealant or socket welded for metals. Threaded fittings can be designed for adapting from a threaded tube to a pneumatic hose or a thread connection to another threaded connection. The threaded connections can be of the same thread with tapered or parallel thread or adapting from a larger thread to a smaller thread.