Flange, also known as a flange boss or rim, 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 devices. A flange connection or flange joint refers to a detachable joint formed by the combination of a flange, a gasket, and bolts. Pipe flanges are the flanges used for piping in pipeline installations, and on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts are used to tightly connect the two flanges. 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 above four kilograms of pressure use welding flanges. A sealing gasket is placed between the two flange discs, and then bolts are tightened. Flange thickness and bolt types vary with pressure ratings. Equipment like pumps and valves, when connected to pipes, have local components shaped as corresponding flanges, also known as flange joints. Any connection component that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as in ventilation pipe connections. These components can be referred to as "flange-type parts." However, such connections are 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."