Experiment with gear ratios on your wind turbine or other small projects. Adding gears to your turbine can greatly increase the generator RPM, giving you higher power output. The small 8-tooth gear fits on 2 mm driveshafts that are found on many DC generators. The gears have a keying feature that allows them to be changed quickly and easily using the included hex locks. The hex lock secures to our 9/64 inch hex-driveshaft. Hex-driveshaft not included.