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, such as reducer flanges. A flange connection or flange joint refers to a removable joint consisting of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are the flanges used in piping installations within equipment, referring to the inlets and outlets of the equipment. Flanges have holes, and bolts secure them tightly together. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamp flanges. Flanges are always used in pairs; low-pressure piping can use threaded flanges, while those above 4 kg pressure use welded flanges. Two flange discs are fitted with a sealing pad and then bolted together. Flange thickness varies with pressure, as do the bolts used. When pumps and valves are connected to pipes, the respective parts of these equipment are also made into flange shapes, 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 connections in ventilation pipes, which can be referred to as "flange-type components." However, such connections are only 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."