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 devices. A flange connection or flange joint refers to a removable connection consisting of a flange, a gasket, and bolts, all working together as a combined sealing structure. Pipe flanges are specifically used for piping in pipe installations, or refer to the inlets and outlets of equipment. Flanges have holes and bolts are used to tightly secure the two flanges. They are sealed using a gasket. Flanges come in threaded (screwed) connections, welding flanges, and clamping flanges. Flanges are used in pairs; low-pressure pipelines can use threaded flanges, while those above 4 kg pressure require welding flanges. Two flange disks are joined with a sealing gasket and then tightened with bolts. Flanges of different pressure ratings have varying thicknesses and require different bolts. In the case of pumps and valves, when connected to pipes, these equipment components are also shaped like corresponding flanges and are called flange connections. Any connection piece that uses bolts to connect and seal two flat surfaces is generally referred to as a "flange," such as in the case of ventilation pipe connections, which can be called "flange-like components." However, such connections are only a part of a device, like the connection between a flange and a pump, so it is not appropriate to call the pump a "flange-like component." Smaller components like valves can be referred to as "flange-like components."