Tee fittings are connectors used at the branch of the main pipeline in the pipeline system. They have three ports (one inlet and two outlets or two inlets and one outlet). They are divided into equal-diameter tees and reducing tees according to the pipe diameter, and can be divided into T-shaped (straight tees) and Y-shaped (oblique tees) according to the branch shape. They are made of more than ten materials including stainless steel, carbon steel, copper, plastic, etc., and are applicable in fields such as chemical industry, construction, petroleum, gas and shipbuilding.