The Pacific-type locomotive evolved as the need for power and speed increased. First, the four-wheel leading truck delivered stability at the faster speeds. Second, six tall drivers provided pulling power and speed. Last, a two-wheel trailing truck provided support for a larger firebox. The sum of this design was the 4-6-2 USRA Pacific.
The USRA designation for light and heavy locomotives was a function of the track's ability to withstand the weight. Excessive axle weight could damage the rails, loosen fastenings, and also cause damage to the locomotive. The USRA deemed a maximum of 54,000 pounds per axle as a light locomotive. The USRA Light Pacific weighed in at 277,000 lbs, with a 73-inch driver diameter and a boiler pressure of 200 lb/in.
BLI's models follow the original designs closely. Railroad specific variations are not modeled on these locomotives. In most instances, they offer two locomotive numbers for each railroad and are offering a painted model (black) with no lettering.