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A street elbow (sometimes called a street ell or service ell) is a type of plumbing or piping fitting intended to join a piece of pipe and another fitting at an angle. The difference between a street elbow and a regular elbow is the nature of the connections on either end.
A regular elbow has a female hub or FIP connection on both ends. A hub is a female ABS, PVC or copper pipe receptacle; FIP denotes "Female Iron Pipe" threads, that is, it receives threaded MIP iron, brass or plastic pipe on both ends. FIP is also known as FPT, Female Pipe Thread, and MIP is also known as MPT, Male Pipe Thread. Collectively, these are known as National Pipe Thread (NPT) fittings.
Instead, a street elbow has a female fitting (hub or FIP) on one end and a male pipe or MIP fitting on the other end. The advantage of the street elbow is that it can be connected directly to another fitting without having to use an additional short connecting piece called a pipe nipple. The "street" nomenclature came from the idea of asking what kind of corner does a male and female meet.
Street elbows are available in 90°, 45° and 22.5° bends. They can be used in water supply, drainage, sewers, vents, central vacuum systems, compressed air and gas lines, HVAC, sump pump drains, and any location where plumbing fittings would be used to join sections of pipe. The Natural Gas and Propane Installation Code of Canada (B149.1) states "...a street elbow or a street tee shall not be used in a piping system".[further explanation needed]