Flange, also known as a flange dish or rim, 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 that consists of a flange, a gasket, and bolts, forming a combined sealing structure. Pipe flanges are flanges used in piping installations, while those used on equipment refer to the equipment's inlet and outlet flanges. Flanges have holes for bolts to secure them tightly, and they are sealed with gaskets. Flanges come in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those over four kilograms of pressure use welding 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. In the case of pumps and valves, the parts that connect to pipes are also shaped as corresponding flanges and are referred to as flange connections. Any connection piece that uses bolts to connect two flat surfaces around the perimeter and seals them is generally called a "flange," such as in ventilation pipe connections. These types of components can be referred to as "flange-type parts." However, such connections are only a part of a single device, 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."