Flange, also known as a flange disc or rim, is a component used for connecting shafts or for pipe ends. It can also be used at equipment inlets and outlets for connecting two devices, such as a reducer flange. A flange connection or flange joint refers to a removable connection that consists 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 inlets and outlets of equipment. Flanges have holes, and bolts secure the two flanges together. They are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding connections, and clamp connections. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those over four kilograms of pressure use welding flanges. Two flange discs are fitted with a sealing pad and then bolted together. Flanges of different pressures have varying thicknesses and require different bolts. Equipment like pumps and valves, when connected to pipes, have corresponding flange shapes for local connections, also known as flange joints. Any connection piece that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as the connections in ventilation pipes. Such components can be referred to as "flange-type parts." However, such connections are only 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 equipment like valves can be called "flange-type parts."