Flange, also known as a flange disc or boss, is a component used for connecting shafts to each other and for joining pipe ends; it is also used at equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable joint consisting of a flange, gasket, and bolt, all interconnected as a combined sealing structure. Pipe flanges are the flanges used for piping in pipeline installations; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure the two flanges together. They are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while pipelines over four kilograms of pressure use welding flanges. A sealing gasket is placed between the two flange discs, and then bolts are tightened. Flanges of different pressures have different thicknesses, and they use different bolts. Pumps and valves, when connected to pipelines, have these equipment parts shaped as corresponding flanges, also known as flange connections. Any connection piece 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 called "flange-type parts." However, this type of connection is 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 referred to as "flange-type parts."