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 at equipment inlets and outlets for connecting two devices, such as a reducer flange. A flange connection or flange joint refers to a removable connection formed by the combination of a flange, a gasket, and bolts. Pipe flanges are flanges used in piping systems, while equipment flanges refer to the inlets and outlets of equipment. Flanges have holes for bolts, which secure the two flanges together, and are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding connections, and clamping connections. Flanges are used in pairs; low-pressure piping can use threaded flanges, while pressures above four kilograms require welding flanges. Two flange discs are joined with a sealing pad and then bolted together. Flange thickness varies with pressure, and so do the bolts used. In the case of pumps and valves, when connected to piping, the local parts of these equipment components are also shaped like flanges and are referred to as flange connections. Any connection piece that uses bolts to connect two flat surfaces and is sealed is generally called a "flange," such as the connection in ventilation piping. Such components can be called "flange-type parts." However, this type of connection is only a part of a device, such as the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type part." Smaller components like valves can be referred to as "flange-type parts."