Flange, also known as a flange disk 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, for connecting two pieces of equipment. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, all interconnected to form a sealing assembly. Pipe flanges are the flanges used in piping installations, and on equipment, they refer to the equipment's inlet and outlet flanges. Flanges have holes, and bolts secure them tightly together. They are sealed with a gasket. Flanges come in threaded (screwed) connections, welded flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those above four kilograms of pressure use welded flanges. Two flange disks are joined with a sealing pad and then bolted together. Flanges of different pressures have different 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 two flat surfaces and is sealed 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 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-type part." Smaller items like valves can be called "flange-type parts."