single pair of axles. American mail cars first appeared in the 1860s and at first followed English design. They had a hook that would catch the mailbag in its crook. As locomotive technology progressed in the mid-19th century, trains grew in length and weight. Passenger cars grew along with them, first getting longer with the addition of a second truck (one at each end), and wider as their suspensions improved. Cars built for European use featured side door compartments, while American car design favored a single pair of doors at one end of the car in the car's vestibule; compartmentized cars on American railroads featured a long hallway with doors from the hall to the compartments. One possible reason for this difference in design principles between American and European carbuilding practice could be the average distance between stations on the two continents. While most European railroads connected towns and villages that were still very closely spaced, American railroads had to travel over much greater distances to reach their destinations. Building passenger cars with a long passageway through the length of the car allowed the passengers easy access to the restroom, among other things, on longer journeys. Dining cars first appeared in the late 1870s and into the 1880s. Until this time, the common practice was to stop for meals at restaurants along the way (which led to the rise of Fred Harvey's chain of Harvey House restaurants in America). At first, the dining car was simply a place to serve meals that were picked up en route, but they soon evolved to include galleys in which the meals were prepared. 1900–1950: Lighter materials, new car types By the 1920s, passenger cars on the larger standard gauge railroads were normally between long. The cars of this time were still quite ornate, many of them being built by experienced coach makers and skilled carpenters. With the 1930s came the widespread use of stainless steel for car bodies. The typical passenger car was now much lighter than its "heavyweight" wood cousins of old. The new "lightweight" and streamlined cars carried passengers in speed and comfort to an extent that had not been experienced to date. Aluminum and Cor-ten were also used in lightweight car construction, but stainless steel was the preferred material for car bodies. It is not the lightest of materials, nor is it the least expensive, but stainless steel cars could