Flange, also known as a flange disc or boss, is a component used for connecting shafts or for joining pipe ends; it is also used on equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a detachable connection made up of the flange, gasket, and bolts as a combined sealing structure. Pipe flanges are flanges used for piping in pipe systems; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes and bolts are used to tightly secure the two flanges together. They are sealed with a gasket. Flanges are available in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure use焊接 flanges. Two flange discs are joined with a sealing pad and then bolted together. Flange thickness and the bolts used vary with pressure ratings. Equipment like pumps and valves, when connected to pipes, have corresponding flange shapes, also known as flange connections. Any connection component that uses bolts to connect two flat surfaces and is sealed is generally called a "flange," such as ventilation pipe connections, which can be referred to as "flange-type components." However, such connections are only a part of a device, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type component." Smaller items like valves can be called "flange-type components."