Rotating unions are used to transfer media from a stationary input to a rotating outlet. They are usually made of brass, bronze, plastic, steel, or stainless steel and include one or more ports which range in size from 1/8 in. to 6 in. Straight ports direct media flow straight through the union. Elbow ports cause the media to exit at an angle from the inlet direction. Seals are made from a variety of materials and feature o-ring and bellows-type designs. Rotating unions connect via flanges or threads and may use dual radial ball bearings to prevent side loading to seals. Flanges are rated by organizations such as the American National Standards Institute (ANSI) and the Society of Automotive Engineers (SAE). Common thread types include national pipe thread (NPT), British standard pipe (BSP), and unified coarse thread (UNC).