Tube fittings are components used for connecting, branching, terminating, and changing the direction of tubing in pneumatic and hydraulic systems. They are made of brass, stainless steel, polybutylene terephthalate (PBT), and other materials that resist corrosion and wear. Tube fittings have various types of connections, including threaded, welded, barbed, and push-to-connect (also called one-touch). Push-to-connect connections do not require tools or sealants. Tube fittings are used in various applications, including machine tools, airplane and truck controls, and automated production lines, among others.