Railroads usually serve both passengers and freight customers. The Arnold rapido model train line had examples of both types of cars used in railroad service. Most of the rapido product line represented German and other European equipment, but Arnold also was interested in the North American market, and produced some equipment for sale here. This was probably at the direction of their U. S. Agent, Charles Merzbach of New York. Some of their American products were adaptations of the German model of a similar car.
European freight cars often were two axle cars and tended to be small. In the case of passenger cars, Arnold manufactured many of its passenger cars that were shorter than normal. This was done because the basic curved track of the early rapido line had a radius of 192 mm (about 7.5 inches), producing a circle of track about 384 mm (about 15 inches). To avoid excessive passenger car overhang on curves, the early passenger cars were manufactured shorter than exact scale length.
Arnold eventually saw the error of their ways and began manufacturing scale length and semi-scale length passenger cars around 1966/1967.