Flange, also known as a flange hub 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 connection consisting of a flange, a gasket, and bolts, forming a combination seal structure. Pipe flanges are flanges used in piping systems within equipment, referring to the inlets and outlets of the equipment. Flanges have holes, and bolts secure the two flanges together. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamping flanges. Flanges are used in pairs; low-pressure piping can use threaded flanges, while flanges for pressures over four kilograms are typically welded. Two flange disks are fitted with a sealing gasket and then fastened with bolts. Flanges of different pressure ratings have varying thicknesses and require different bolts. Pumps and valves, when connected to pipes, have locally shaped flanges to match, also known as flange connections. Any connection piece that uses bolts to connect and seal two flat surfaces is generally called a "flange," such as the connection in ventilation pipes, which can be referred to as "flange-type components." 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 component." Smaller items like valves can be referred to as "flange-type components."