In the U.S. flanges are either threaded or welded onto the pipe. The term "flange" is also used for a kind of tool used to form flanges. The hub shell typically has two machined metal flanges to which spokes can be attached. In the European market flanges are usually welded onto the pipe. Connection methods include threadings, compression fittings, glue, cement, flanges, or welding. The LEBU includes two identical circumferential airfoils and two flat flanges. A copper ring gasket is used with conflat flanges. Shafts were usually rigid steel, made up of several parts bolted together at flanges. Non-metallic gaskets are used with flat- or raised-face flanges. There are many standards in gasket for flanges of pipes. A reaction torque sensor has two mounting flanges. The heat exchanger was a shell assembly, consisting of a duct, bellows, flanges, and coils. Screw-propelled vehicles are propelled by auger-like cylinders fitted with helical flanges. Pipes with flanges can be assembled and disassembled easily. One solution was to remove or thin the flanges on an axle.