Flange, also known as a flange disc or raised boss. A flange is a component that connects two shafts, used for joining pipe ends; 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 the detachable connection of a combination sealing structure, consisting of the flange, gasket, and bolt. Pipe flanges are the flanges used for piping in pipeline systems; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly together. Seals are used between flanges. Flanges are categorized into threaded connection (threaded flange), welded flange, and clamp flange. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while pipelines with pressures above 4 kg require welded flanges. A sealing pad is placed between the two flange discs, and then bolts are tightened. Flanges of different pressures have varying thicknesses and require different bolts. In the case of pumps and valves, when connected to pipelines, the local parts of these equipment items are also made into corresponding flange shapes, also known as flange joints. Any connection piece that uses bolts to connect two flat perimeters and is sealed is generally called a "flange," such as the connection of ventilation pipes. Such components can be referred to as "flange-type parts." However, such connections are only a part of a single device, such as the connection between a flange and a pump, so it is not appropriate to call the pump a "flange-type part." Smaller items like valves can be called "flange-type parts."