Flange, also known as a flange disc or boss, is a component used for connecting shafts or for pipe ends. It is also used at equipment inlets and outlets for connecting two devices, such as reducer flanges. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, which together form a combined sealing structure. Pipe flanges are flanges used in piping installations; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes and bolts are used to tightly secure the two flanges. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamping flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use welded flanges. Two flange discs are joined with a sealing pad and then bolted together. Flanges of different pressures have different thicknesses and require different bolts. Pumps and valves, when connected to pipelines, have locally shaped 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 in the case of ventilation pipeline connections. Such components can be referred to as "flange-type parts." However, this type of connection is only a part of a device, such as 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."