Flange, also known as a flange disk or boss, is a component used for connecting shafts to each other or for joining pipe ends; it is also used at equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable connection that consists of a flange, a gasket, and bolts, forming a combination sealing structure. Pipe flanges are flanges used for piping in pipeline installations; when used on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts are used to tightly connect the two flanges. Gaskets are used to seal between flanges. Flanges are available in threaded (screwed) connections,焊接 (welded) flanges, and clamping flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use welding flanges. Two flange disks are fitted with a sealing pad and then secured with bolts. Flanges of different pressures have different thicknesses and require different bolts. In the case of pumps and valves, when connected to pipelines, the local parts of these equipment items are also made into 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 the connection of ventilation pipes, which can be referred to as "flange-type components." However, such connections are only a part of a device, such as the connection between a flange and a pump, so it is not appropriate to call the pump a "flange-type component." Smaller items like valves can be called "flange-type components."