Flange, also known as a flange disc or boss, is a component used for connecting shafts or for joining pipe ends. It is also used at equipment inlets and outlets, such as reducer flanges, for connecting two pieces of equipment. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are the flanges used for piping in pipe systems, or refer to the inlet and outlet flanges on equipment. Flanges have holes, and bolts secure them tightly. Gaskets are used to seal between flanges. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure use焊接 flanges. Two flange discs are joined with a sealing pad and then bolted together. Flanges of different pressures have different thicknesses and require different bolts. In the connection of equipment like pumps and valves to pipelines, the respective parts are also made in flange shape, known as flange connections. Any connection piece that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as in ventilation pipe connections. Such components can be referred to as "flange-type parts." However, such connections are only a part of a single 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."