Flange, also known as a flange disk or boss, is a component that connects two shafts or is used for pipe end connections; it can also be used on equipment inlets and outlets for connecting two devices, such as a reducer flange. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, forming a combined sealing structure. Pipe flanges are flanges used for piping in pipeline installations; on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure the two flanges together. They are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg of pressure use welding flanges. A sealing pad is placed between the two flange disks, then secured with bolts. Flanges of different pressures have different thicknesses and require different bolts. In the connection of equipment like pumps and valves to pipelines, the local parts of these equipment are also made into corresponding flange shapes, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces around the periphery and is sealed simultaneously is generally called a "flange," such as the connection of ventilation pipes, which can be referred to as "flange-type components." 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 component." Smaller components like valves can be called "flange-type components."