The "Six-Pack" Starter Set is an economical way to test different gear ratios and find the optimum ratio for you and your machine before buying lightened and hardened premium steel or aluminum pinions. There are six different precision-cut steel pinions in each set, one set of even numbered teeth and one set of odd numbered teeth, see below for sizes. "Six-Pack" gears are not heat treated or plated so we recommended you use them with plastic spur gears.