Flange, also known as a flange disc or boss, is a component used for connecting shafts or for joining pipe ends. It is also used on equipment 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, which together form a combination seal 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. 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 four kilograms of pressure use welded flanges. Two flange discs are fitted with a sealing pad and then bolted together. Flanges of different pressures have different thicknesses and require different bolts. In the case of pumps and valves, when connected to pipelines, these equipment parts 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 circumference and is sealed is generally called a "flange," such as the connection of ventilation pipes. Such components can be referred to as "flange-type parts." However, such connections are 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."