MTH: 30-75735 RailKing Union Pacific 4-Bay Cylindrical Hopper Car #21214 O Gauge Until the advent of the covered hopper, bulk commodities like grain and cement were packed in sacks and loaded into boxcars. Loading and unloading was a tedious, time-consuming affair. In the 1930s, a few railroads took the basic coal hopper design and added a roof with loading hatches, enabling bulk commodities to be loaded from the top and unloaded from the bottom. In 1953, Pullman-Standard’s 70-ton PS-2 became the first mass-produced covered hopper to be widely owned by U.S. railroads.But these pioneering covered hoppers had one problem: Like other cars of their time, they were built on a frame with a center sill, or support beam, that ran down the middle. Some of the load would cake or collect on the beam, making it difficult to fully unload the cars. In 1961, American Car and Foundry solved the problem with the first center-flow covered hopper, with its support beams on the outside of the frame and unobstructed, full-width unloading doors. Today’s cylindrical hoppers are all descended from that ACF innovation. Our model represents a modern 100-ton, 4-bay car designed for lighter density loads like grains and plastic pellets; denser commodities are generally shipped in 2- or 3-bay cars.High quality, traditionally sized RailKing Freight Cars provide detailed bodies and colorful paint schemes for the O Gauge railroader. MTH makes an enormous variety of RailKing Freight Cars, including many different car types and roadnames. No matter what era or part of the country you are modeling, RailKing is sure to have something for you.