Hose and pneumatic tubing unions are used to securely fasten two hoses or tubes together. They are durable devices that resist leaks, high-pressure flow, corrosion, and wear. Hose and pneumatic tubing unions come in hammer unions and standard unions. Hammer unions typically come in threaded or O-ring forms, while standard unions come in barbed, compression-nut, crimp-on, threaded, and O-ring forms. Both hammer and standard unions also come in different shapes, such as elbow, Y, and tee.