Flange, also known as a flange boss or rim, is a component that connects shafts together and is used for joining pipe ends. There are also flanges used at equipment inlets and outlets for connecting two pieces of equipment, such as a reducer flange. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts that form a combined sealing structure. Pipe flanges are the flanges used for piping in pipe systems; on equipment, they refer to the inlets and outlets of the equipment. Flanges have holes for bolts, which secure the two flanges together. They are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding connections, and clamping connections. Flanges are always used in pairs; low-pressure piping can use threaded flanges, while pressures over four kilograms require welding flanges. A sealing gasket is placed between two flange disks, then secured with bolts. Flanges of different pressures have different thicknesses and require different bolts. Pumps and valves, when connected to pipes, have corresponding flange shapes for these equipment components, also known as flange connections. Any connection component that uses bolts to join two flat surfaces around the perimeter and seal them is generally called a "flange," such as the connection of ventilation pipes, which can be referred to as "flange-like components." However, this type of connection is 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 component." Smaller items like valves can be referred to as "flange-like components."