Metal fittings are essential connectors in industrial piping systems, primarily used for sealing connections between pipes, hoses, or equipment. Common materials include stainless steel, brass, and carbon steel, and they can be categorized by structure into threaded, flanged, and quick-connect types. Stainless steel fittings offer strong corrosion resistance and are suitable for the chemical industry; brass fittings have good electrical conductivity and are often used in electrical equipment; carbon steel fittings offer high strength.