Flange, also known as a flange disk or boss, is a component used for connecting shafts to each other, typically for pipe end connections; it is also used on equipment for connecting two devices, such as a reducer flange. A flange connection or flange joint refers to a removable joint consisting of a flange, a gasket, and bolts, forming a combination sealing structure. Pipe flanges are the flanges used in piping installations, and 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 are categorized into threaded connection (threaded flanges), welded flanges, and clamping flanges. Flanges are always used in pairs; low-pressure piping can use threaded flanges, while pressures above four kilograms require welded flanges. Two flange disks are joined with a sealing gasket and then tightened with bolts. Flanges of different pressures have varying thicknesses and require different bolts. In the case of pumps and valves, when connected to pipes, these equipment components are also made in a corresponding flange shape, known as flange connections. Any connection that uses bolts to connect two flat surfaces around the perimeter and is sealed is generally called a "flange," such as the connection in ventilation pipes. Such components can be referred to as "flange-type parts." However, such a connection is 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 referred to as "flange-type parts."