A flange is a component used to connect shafts to each other or to connect pipe ends; there are also flanges used at equipment inlets and outlets for connecting two devices, such as a reducer flange.

Flange connection or flange joint refers to a removable joint composed of a flange, a gasket, and bolts that connect as a set of combined sealing structure. The flange has holes, and the bolts secure the two flanges together. A gasket is used to seal between the flanges. Flanges are categorized into threaded (screwed) flanges, welding flanges, and clamp flanges.

Flanges are used in pairs. For low-pressure piping, threaded flanges can be used, while for pressures above four kilograms, welding flanges are recommended. A gasket is placed between the two flange discs and then secured with bolts. Flanges of different pressures have varying thicknesses and require different bolts. Pumps and valves, when connected to pipes, have local parts shaped to match the flange, which is also known as a flange connection. 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. Such components can be referred to as "flange-type parts." However, this type of 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 items like valves can be called "flange-type parts."