This package of 60 gears provides you with a great assortment of our 3 most popular gear teeth options. 10, 30 and 50 tooth gears! These gears have a 4mm hole. Use the bushings to convert the 4mm hole to a 2mm to fit a motor spindle. This pack is great for any project requiring unique gear sizes and teeth. Great for making your own gear box or gear driven car or turntable.