Flange, also known as a flange dish or boss, is a component used for connecting shafts to each other, typically for pipe end connections; it is also used on equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable connection made up of the flange, gasket, and bolts, forming a combined sealing structure. Pipe flanges are the flanges used for piping in pipe installations; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly. 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 piping can use threaded flanges, while pressures above four kilograms require焊接 flanges. Two flange disks are joined with a sealing pad and then bolted together. Flange thickness varies with pressure, as do the bolts used. When pumps and valves are connected to pipes, the local parts of these equipment items are also made into corresponding flange shapes, 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 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 device, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type part." Smaller items like valves can be called "flange-type parts."