Flange, also known as a flange collar or boss. A flange is a component used to connect two shafts or to join pipe ends; it is also used at equipment inlets and outlets for connections between two pieces of equipment, such as a reducer flange. Flange connection or flange joint refers to a detachable connection consisting of the flange, gasket, and bolts connected together as a sealing assembly. Pipe flanges are flanges used in piping systems; when used on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes and bolts are used to securely fasten the two flanges together. Gaskets are used to seal the gaps between flanges. Flanges come in threaded (screwed) connections, welding connections, and clamping connections. Flanges are used in pairs; low-pressure piping can use threaded flanges, while pressures above four kilograms require welding flanges. A sealing gasket is placed between two flange discs, then secured with bolts. Flange thickness varies with pressure, and so do the bolts used. When connecting pumps and valves to piping, the equipment's local components are often shaped to match the flange design, also known as flange connections. Any connection component used to fasten two flat surfaces with bolts and seal them is generally called a "flange," such as in the case of ventilation pipe connections, these components can be referred to as "flange-type components." However, this type of connection is only a part of a single piece of equipment, like the connection between a flange and a pump, so it's not appropriate to call the pump a "flange-type component." Smaller components like valves can be called "flange-type components."