Flange, also known as a flange boss or hub. A flange is a component used for connecting shafts to each other, serving for pipe end connections; there are also flanges used at equipment inlets and outlets for connecting two devices, such as reducer flanges. Flange connection or flange joint refers to the detachable connection formed by the combination of flanges, gaskets, and bolts as a sealed structure. Pipe flanges are flanges used in piping installations; when used on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure the two flanges together. Gaskets are used to seal between flanges. Flanges are categorized into threaded connection (threaded flange), welding flange, and clamping flange. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use welding flanges. Two flange disks are joined with a sealing gasket and then bolted together. Flange thickness and bolt types vary with pressure ratings. Equipment like pumps and valves, when connected to pipes, have corresponding flange shapes, also known as flange joints. Any connection component that uses bolts to connect and seal two flat surfaces is generally called a "flange," such as the connection of ventilation pipes, which can be referred to as "flange-like components." However, such connections are only part of a device, like the connection between a flange and a pump, so it's not appropriate to call the pump "flange-like components." Smaller devices like valves can be called "flange-like components."