Flange, also known as a flange disc or boss, 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 pieces of equipment. A flange connection or flange joint refers to a removable connection made up of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are flanges used in piping installations, and on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly together. They are sealed with a gasket. Flanges come in threaded (screwed) connections,焊接 (welded) flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use焊接 flanges. Two flange discs are fitted with a sealing pad and then secured with bolts. Flanges of different pressures have different thicknesses and require different bolts. In the case of pumps and valves, when connected to pipes, these equipment components are also shaped to match the flange, also known as a flange connection. Any connection piece that uses bolts to connect two flat surfaces around the periphery and is sealed is generally called a "flange," such as the connection of ventilation pipes. Such components can be referred to as "flange-type parts." However, this type of connection is only a part of a single piece of equipment, 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."