Flange, also known as a flange disc or boss, is a component used for connecting shafts to each other, typically for pipe end connections; it is also used on equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable connection formed by the combination of flange, gasket, and bolt, serving as a seal structure. Pipe flanges are the flanges used for piping in pipe installations, or for equipment inlets and outlets on equipment. Flanges have holes, and bolts are used to tightly secure the two flanges. They are sealed with a gasket. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamping 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 disks are joined with a sealing pad and then bolted together. Flanges of different pressures have varying thicknesses and require different bolts. Equipment like pumps and valves, when connected to pipes, have local parts shaped as corresponding flanges and are also called flange connections. Any connection piece that uses bolts to connect two flat surfaces and seal them is generally referred to as a "flange," such as in ventilation pipe connections. Such components can be called "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 referred to as "flange-type parts."