Flange, also known as a flange disk or boss, is a component used for connecting shafts to each other, typically for pipe end connections; it is also used on equipment for connecting two devices, such as a reducer flange. A flange connection or flange joint refers to a removable joint that consists of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are those used in piping systems, while equipment flanges refer to the inlets and outlets of the equipment. Flanges have holes, and bolts secure them tightly. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure require welding flanges. Two flange disks are joined with a sealing pad and then fastened with bolts. Flanges of different pressures have varying thicknesses and require different bolts. Pumps and valves, when connected to pipes, have corresponding flange shapes for these equipment components, also known as flange connections. Any connection component that uses bolts to connect two flat surfaces 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, this type of connection is 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 referred to as "flange-type parts."