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 detachable connection consisting of a flange, a gasket, and bolts, which together form a combination sealing structure. Pipe flanges are flanges used in piping installations, while those on equipment refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure the two flanges together. Gaskets are used to seal between flanges. Flanges come in threaded (screwed) connections,焊接 (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焊接 flanges. Two flange discs are fitted with a sealing pad and then secured with bolts. Flanges of different pressures have varying thicknesses and require different bolts. Pumps and valves, when connected to pipes, have locally shaped flanges that correspond to these equipment connections, also known as flange joints. Any connection piece that uses bolts to connect two flat surfaces around the perimeter and is sealed is generally called a "flange," such as the connection of ventilation pipes, which can be referred to as "flange-like components." However, such connections are only a part of a device, like the connection between a flange and a pump, making it inappropriate to call the pump a "flange-like component." Smaller items like valves can be called "flange-like components."