This is a replacement drive for the virtually identical Custom Brass and Balboa HOn3 C-21s that were imported some 60 years ago (the amount of time between when these models were imported to the present day is longer than when the real CRR/D&RGW C-21s were built by Baldwin to when the models were imported!) This drive does two things, it decreases the speed of the model while proportionately increasing pulling power. The gears add 2.4:1 reduction giving you a final reduction of 72:1 with a coreless motor that runs at 13500 RPM @ 12VDC. This combination provides a much better overall speed range with a top speed of ~35MPH. Installation is relatively straight forward. The unit is designed to exactly fit the existing mounting plate using the existing screws. Given the age of the models, some careful cleaning and lubrication is likely in order as well as some gentle filing of the slot on the bottom of the boiler.