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, which together form a sealing assembly. Pipe flanges are those used for piping in pipe assemblies; 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. Gaskets are used to seal the flanges. 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 above 4 kg pressure use welded flanges. Two flange discs are fitted with a sealing gasket and then secured with bolts. Flange thickness and bolt types vary depending on pressure ratings. Equipment like pumps and valves, when connected to pipes, have corresponding flange shapes at their connection points, also known as flange connections. Any connection piece that uses bolts to join two flat surfaces around the periphery and is sealed is generally called a "flange," such as in ventilation pipe connections. Such components can be referred to as "flange-type parts." However, this type of connection is only a part of a single 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 referred to as "flange-type parts."