Flange, also known as a flange dish or boss, 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 flanges used for piping in pipe systems; when used 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. A gasket is used to seal the gap between flanges. Flanges come in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipes can use threaded flanges, while pipes over four kilograms of pressure use welding flanges. Two flange disks are placed with a sealing pad in between, then bolted together. Flanges of different pressure ratings have different thicknesses and require different bolts. When connecting pumps and valves to pipes, the parts of these equipment are also made into corresponding flange shapes, known as flange connections. Any connection that uses bolts to connect two flat surfaces and seal them is generally called a "flange," such as the connection of ventilation pipes. Such parts 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."