Elbow is a pipe fitting installed between two lengths of pipe or tube allowing a change of direction, usually 90° or 45°. The ends may be machined for butt welding, threaded or socketed. When the two ends differ in size, it is called a reducing or reducer elbow. It is used change the direction of the pipe and have a close radius to fit in the tightest possible space. The most commonly used elbows are 90 and 45-radius elbow. Most elbows are available in short radius or long radius of types. The short radius elbows have a center to end distance equal to the NPS in inches, while the long radius is 1.5 times the NPS in inches.