10, 11, 12, 13 and 14 tooth mod 0.5 pinions selected to compliment the Scorpion HK22 series motors - mod .5 is used on most 400, 450 and 480 class electric helicopters. These pinions are designed to fit any motor with a 3.175mm shaft (1/8 inch), and come with an allen key set screw (one pinion & allen key per pack).