Flange, also known as a flange disk or boss, is a component used for connecting shafts to each other 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, which together form a combined sealing 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 always used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use焊接 flanges. Two flange disks are sealed with a gasket and then bolted together. Flange thickness varies with pressure, as do the bolts used. In the case of pumps and valves, when connected to pipes, these equipment components are also made in corresponding flange shapes, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces and is sealed simultaneously is generally called a "flange," such as the connection of ventilation pipes. Such parts can be referred to as "flange-type parts." However, this type of connection is only a part of a single device, such as the connection between a flange and a pump, so it is not appropriate to call the pump a "flange-type part." Smaller items like valves can be called "flange-type parts."