Another beautifully-constructed small milling machine, the Pratt &Whitney 3C is sometime found with the desirable infinitely variable-speed drive system manufactured by the "Master Electric Co." Called the "Speedranger", the unit drove to the spindle using twin V-belts and offered speeds from 125 to 2250 rpm. Typical of the type first offered in this miniature form from the 1920s, the variation in output speed was achieved by a pair of expanding and contracting V-pulleys connected by a steel chain-link belt running in an oil bath . The unit was neatly designed and heavily built; a specially-made, cast-iron frame 2-speed motor was used (with an integral support bracket) mounted end-on to the speed changer; the  both units being fastened to a heavy metal plate slung, in the case of the 3C miller, beneath the bench. In order to make the unit suitable for as wide a range of applications as possible the position of the variable-speed pulleys were altered through a worm-and-wheel mechanism driven by a cable held within a flexible conduit..