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 at equipment inlets and outlets, such as reducer flanges. 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 the flanges used in piping installations, while on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes and bolts are used to tightly secure the two flanges together. Gaskets are used to seal between flanges. Flanges are available in threaded (screwed) connections,焊接 (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焊接 flanges. A sealing pad is placed between the two flange discs, and then bolts are tightened. Flanges of different pressures have different thicknesses and require different bolts. When pumps and valves are connected to pipelines, the local parts of these equipment items are also made into corresponding flange shapes, also known as flange connections. Any connection piece that uses bolts to connect two flat surfaces and seal them 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 local part of a device, such as 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."