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 on equipment inlets and outlets, such as reducer flanges, for connecting two pieces of equipment. Flange connection or flange joint refers to a removable joint that consists of a flange, a gasket, and bolts, forming a combined sealing structure. Pipe flanges are flanges used in piping systems, while those used on equipment refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly together. They are sealed with a gasket. 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 4 kg pressure use welded flanges. A sealing pad is placed between the two flange discs, and then bolts are used to secure them. Flanges of different pressures have different thicknesses, and thus, different bolts are used. In the case of pumps and valves, when connected to pipes, these equipment components are also shaped to match the flange design, also known as flange connections. Any connection component used for bolting together two flat surfaces around the circumference is generally called a "flange," such as in the case of ventilation pipe connections. Such components can be referred to as "flange-type components." 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 component." Smaller components like valves can be called "flange-type components."