The AtlasO Premier 2-rail O Scale ACF 3-Bay Center-Flow Covered Hopper is based on some of the most widely used cars in service since the late 1960s. Although covered hoppers had achieved widespread use by the 1950s, it wasn't until the following decade that they began to carry North America's grain harvest. Prior to the 1960s, U.S. and Canadian farmers sent their wheat and other grains to market in 40' boxcars. Loading and unloading was labor-intensive and time-consuming. All that changed with American Car and Foundry's (ACF's) introduction of the Center Flow covered hopper in 1961, followed the next year by Pullman-Standard's competitive PS-2CD covered hopper. Prior to the Center Flow, the typical covered hopper was little more than a coal hopper with a roof. Dry products such as salt were loaded through roof hatches and unloaded by gravity through doors in the floor. Like most freight cars of their era, these cars had a center sill. This support beam ran down the middle of the car between the left and right sets of unloading doors, and that led to problems in emptying the car. Typically some of the load would cake or |bridge} on the center sill, and the car would have to be vibrated to loosen the mess and achieve full unloading. Of course the vibration tended to shorten the life of the car. The Center Flow's key innovation was the elimination of the center sill by relocating the car's main support beams to the bottom edge of each side. This enabled the discharge hopper doors to be located along the centerline of the car, allowing for easier, more complete unloading. In addition, the car sides were curved to allow for more complete filling of the car. The Center Flow was the first larger-capacity covered hopper designed for grain and products of similar density. By the 1980s, ACF's Center Flow, along with covered grain hoppers from other builders, had spelled the end of the 40' boxcar in grain service. In addition to grain, the Center Flow found work hauling a variety of other light to medium-density dry commodities, including salt, clay, chemicals, phosphates and other minerals. This model features accurate details, separately applied brake details, roller-bearing with free-rolling metal wheelsets, fine paint, crisp lettering and knuckle couplers. Decorated in classic or later schemes, the ACF 3-Bay Center-Flow Covered Hopper is perfect for your diesel-era freight consists. Check out the entire line of AtlasO freight cars.