Flange, also known as a flange disk or boss, is a component used for connecting shafts to shafts, typically 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 detachable connection formed by the combination of flange, gasket, and bolt. Pipe flanges are 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 secure the two flanges together. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure require welded 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. When pumps and valves are connected to pipelines, the respective parts of these equipment are also shaped like flanges, known as flange connections. Any connection piece that uses bolts to connect two flat surfaces around the periphery and seals them is generally called a "flange," such as in the connection of ventilation pipes. Such components can be referred to as "flange-like parts." However, this type of connection is only a part of a single piece of equipment, such as the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-like part." Smaller items like valves can be called "flange-like parts."