Flange, also known as a flange disc 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 devices. A flange connection or flange joint refers to a removable connection formed by the combination of a flange, a gasket, and bolts. Pipe flanges are the flanges used for piping in pipe installations, or the inlets and outlets of equipment. Flanges have holes, and bolts secure them tightly. 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 4 kg of pressure use welded flanges. Two flange discs are joined with a sealing pad and then bolted together. Flanges of different pressures have different thicknesses and require different bolts. In the connection of equipment like pumps and valves to pipes, the local parts of these devices are also made in the shape of corresponding flanges, 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 components can be referred to as "flange-type parts." However, such a 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 components like valves can be called "flange-type parts."