19-tooth pinion gear (1.0 metric pitch) fits 5 mm motor shafts and includes set screw. (For use with steel spur gears) Traxxas pinion gears let you fine-tune the performance of your Traxxas model. Changing gear ratios can help balance acceleration and top speed for different running conditions. Please consult your owner’s manual for more information on recommended gearing options for your specific model.