The 90 degree elbows are used to connect tubes at a 90° angle. As the name suggests, the elbow is always a right-angle in shape. Such type of elbow is also known as "90 bends or 90 ells". This is a pipe fitting device that is bent in such a way to produce a 90° change in the direction of flow of the fluid/gas in the pipe. The elbow is used to change the direction in piping and is also sometimes called a "quarter bend http://www.zhijusteel.com/elbow/90-degree-elbow/