The 500 WM 20 was produced by British company BSA (Birmingham Small Arms) between 1937 and 1955. An extremely solid bike, it was powered by a 496 cc single-cylinder four-stroke engine. This bike was designed in both a military and civilian version, retaining broadly similar characteristics. The civilian version was excellent for tourism and transport (the version with sidecar proved popular). The cast iron engine manufactured for the military models from 1945 onwards was maintained until 1951, the only modification being the introduction of an alloy cylinder head. The high performance and features of the BSA 500 made it an extremely precious model which is sought after by collectors all over the world.