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 detachable connection that consists of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are those used for piping in pipe installations, and when used on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes and bolts are used to tightly secure the two flanges 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 pipelines can use threaded flanges, while those over four kilograms of pressure use welded 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 pumps and valves, when connected to pipes, these equipment parts are also made into corresponding flange shapes, known 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 of ventilation pipes. Such parts 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 components like valves can be called "flange-type components."