Flange is also called a flange plate or protruded rim. It is a connecting part between flange shaft and shaft, which is used for the connection between pipe ends; it can also be used as the flange at the inlet and outlet of the equipment for the connection between two equipment, such as reducer flange. Flange connection or flange joint refers to the removable connection of a group of combined sealing structures composed of flanges, gaskets and bolts. Pipe flange refers to the flange used in pipe fittings, and the flange used in equipment refers to the inlet and outlet flanges of equipment. There are holes in the flange, and the bolts make the two flanges closely connected. Flanges are sealed with gaskets. Flanges are divided into threaded (screwed) flange, welded flange and clamp flange. Flanges are used in pairs. Threaded flange can be used for low-pressure pipeline, and welded flange can be used for pressure above 4kg. A washer is added between the two flanges, and then the flanges are fastened with bolts. The flange thickness is different under different pressures, and the bolts used are also different. When the water pump and valve are connected with the pipeline, the parts of these equipment are also made into the corresponding flange shape, also known as flange connection. All connecting parts bolted and enclosed around two planes are generally called "flanges", such as the connection of ventilation pipes. Such parts can be called "flange parts". However, this connection is only a part of the equipment, such as the connection between the flange and the water pump, so it is difficult to call the water pump a "flange part". Smaller, such as valves, can be called "flange parts".

Reducer flange is used for connection between motor and reducer and between reducer and other equipment.