Flange, also known as a flange collar or rim, is a component used for connecting shafts to each other or for joining pipe ends; it is also used at equipment inlets and outlets, such as reducer flanges. A flange connection or flange joint refers to a removable joint formed by the combination of flanges, gaskets, and bolts. Pipe flanges are specifically the flanges used for piping in pipeline installations, or refer to the inlets and outlets of equipment. Flanges have holes and bolts that secure them tightly together. They are sealed with gaskets between them. 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 over four kilograms of pressure require welding flanges. Two flange disks are fitted with a sealing pad and then bolted together. The thickness of flanges varies with pressure, as do the bolts used. In the case of pumps and valves, when connected to pipes, these equipment parts are also made into corresponding flange shapes, known as flange joints. Any connection component that uses bolts to connect two flat surfaces around the periphery and is sealed simultaneously is generally called a "flange," such as the connections in ventilation ducts. These types of components can be referred to as "flange-like 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-like part." Smaller items like valves can be called "flange-like parts."