Flange, also known as a flange disk or boss, is a component used for connecting shafts or for joining pipe ends. It is also used on equipment for connecting two devices, such as a reducer flange. Flange connections or flange joints refer to a detachable connection made up of the flange, gasket, and bolts, acting as a combined sealing structure. Pipe flanges are those used in piping systems, while equipment flanges refer to the inlets and outlets of the equipment. Flanges have holes, and bolts secure them tightly. 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 disks are joined with a sealing gasket and then fastened with bolts. Flanges of different pressures have different thicknesses and require different bolts. When pumps and valves are connected to pipes, these equipment parts are also shaped like flanges and are called flange connections. Any connection piece that uses bolts to join and seal two flat surfaces is generally referred to as a "flange," such as in the connection of ventilation pipes. Such components can be called "flange-type parts." However, this type of connection is only a part of a device, such as 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."