Flange, also known as a flange disc or boss, is a component used for connecting shafts to each other, typically for pipe end connections; it is also used on equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, all interconnected to form a combined sealing structure. Pipe flanges are flanges used in piping installations, while equipment flanges refer to the inlets and outlets of equipment. Flanges have holes, and bolts secure them tightly together. They are sealed with a gasket. Flanges come 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. A sealing pad is placed between the two flange discs, and then bolts are used to tighten them. Flange thickness varies with pressure, as do the bolts used. In the case of pumps and valves, when connected to pipes, these equipment components are also shaped to correspond to flanges, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as the connection of ventilation pipes. These types of components can be referred to as "flange-type components." However, such connections are only a part of a single piece of equipment, 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."