Pipe Tee, Tee Fittings 

A tee is also called triplet,three way and "T" pieces and it can be used to either combine or split a fluid flow. Most common are tees with the same inlet and outlet sizes, but 'reducing' tees are available as well. it means the one or two ends are differ in dimension.due to this dimension differ,the makes the tee fittings with the capacity to control the volume when required.