Screw fittings are components to connect/branch pipes for fluids such as liquid, air and gas. They include elbows to change the pipe direction to 90 degrees, bushings to connect male and female threads with different diameters, tees and cross fittings for T/cross-shaped branching and sockets for the pipe connection between male threads. Materials of screw fittings must be appropriate for the fluid used, and basically need to come in the same as their pipe counterparts. Stainless steel with excellent resistance to water, oil and corrosion is used for water, oil and gas pipes; resin with excellent resistance to fatigue, creep and heat is used for water and oil pipes. In addition, considering that PVC is suitable for water and air, steel for air, oil and gas, copper for air, water and oil, fitting materials must be selected appropriately for each operating environment.