 The companies involved were Birmingham RC&W, Gloucester RC&W and Metro-Cammell, although the units supplied were of near-identical external appearance, and fitted with the same equipment.Each company provided a three-car and a four-car unit, the three-car unit consisting of a trailer car with a driving motor car at both ends, and the four-car units being of similar formation, but with an additional non-driving motor car in the rake.While they were similar in many respects to the 1938 stock, the main differences were that the body panels were unpainted aluminium, rather than painted steel, a rubber suspension system was used on the bogies, reducing the number of parts that required regular maintenance, and the lighting was provided by fluorescent tubes, rather than incandescent bulbs.