23-tooth pinion gear (1.0 metric pitch) fits 5 mm motor shafts and includes set screw. Designed for 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 owners manual for more information on recommended gearing options forIncludes:(1) Set ScrewThis product is compatible with the following Model(s): Traxxas Maxx,Traxxas XRT