Flange, also known as a flange disc or rim, is a component used for connecting shafts 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 combined sealing structure. Pipe flanges are flanges used in piping systems within equipment, specifically referring to the inlet and outlet flanges of the equipment. 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, welding connections, and clamp 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, as do the bolts used. In the case of pumps and valves, when connected to pipes, the local parts of these equipment components are also made into corresponding flange shapes, 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 part of a single piece of equipment, like the connection between a flange and a pump, so it is not appropriate to call the pump a "flange-type component." Smaller components like valves can be called "flange-type components."