Flange, also known as a flange boss or rim, is a component that connects shafts to each other, used for pipe end connections; there are also flanges used at equipment inlets and outlets for connecting two devices, such as reducer flanges. Flange connection or flange joint refers to a removable connection made up of the flange, gasket, and bolt, forming a combined sealing structure. Pipe flanges are flanges used for piping in pipe systems; when used on equipment, they 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 are categorized into threaded (screwed) flanges, welded flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use welded flanges. A sealing gasket is placed between the two flange discs, and then bolts are tightened. Flanges of different pressures have different thicknesses, and they use different bolts. Pumps and valves, when connected to pipes, the local parts of these equipment items are also made into corresponding flange shapes, also known as flange connections. Any connection component that uses bolts to connect two flat surfaces around the periphery and is sealed is generally called a "flange," such as the connection of ventilation pipes, these types of components can be called "flange-type components." However, this type of connection is only a part of a device, such as the connection between a flange and a pump, it is not appropriate to call the pump a "flange-type component." Smaller items like valves can be called "flange-type components."