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, for connecting two devices. 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 installations, while those on equipment refer to the equipment's inlet and outlet flanges. Flanges have holes for bolts, which secure the two flanges together, and are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure require welded flanges. Two flange discs are joined with a sealing pad and then bolted together. Flange thickness and bolt types vary with pressure ratings. Equipment like pumps and valves, when connected to pipes, have corresponding flange shapes, known as flange connections. Any connection that uses bolts to join two flat surfaces and seal them is generally called a "flange," such as in ventilation pipe connections. Such components can be referred to as "flange-type parts." However, such connections are only a 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 part." Smaller items like valves can be called "flange-type parts."