Flange, also known as a flange dish 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 that consists of a flange, a gasket, and bolts, forming a combination sealing structure. Pipe flanges are flanges used for piping in pipeline installations, while equipment flanges refer to the inlets and outlets of equipment. Flanges have holes and bolts are used to tightly connect them. They are sealed with a gasket. Flanges are available in threaded (screwed) connections, welding flanges, and clamp flanges. Flanges are always used in pairs; low-pressure pipelines can use threaded flanges, while those over 4 kg of pressure require welding flanges. Two flange disks are fitted with a sealing pad and then secured with bolts. Flange thickness and the type of bolts used vary with pressure ratings. Pumps and valves, when connected to pipes, have locally shaped flanges corresponding to these equipment connections, also known as flange connections. Any connection component that uses bolts to connect two flat surfaces around the perimeter and is sealed is generally called a "flange," such as in ventilation pipe connections. These components can be referred to as "flange-type parts." However, such connections are only 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 part." Smaller items like valves can be referred to as "flange-type parts."