Flange, also known as a flange disc or boss, is a component used for connecting shafts to shafts, 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 made up of the flange, gasket, and bolts, forming a combined sealing structure. Pipe flanges are flanges used for piping in pipe systems, or for equipment inlets and outlets on equipment. Flanges have holes, and bolts secure the two flanges together. They are sealed with a gasket. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure use焊接 flanges. Two flange discs are fitted with a sealing pad and then bolted together. Flanges of different pressures have different thicknesses and require different bolts. When pumps and valves are connected to pipes, the local parts of these equipment components are also made into corresponding flange shapes, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces around the perimeter and is sealed is generally called a "flange," such as the connection of ventilation pipes. Such parts can be referred to as "flange-type parts." However, this type of 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 components like valves can be called "flange-type parts."