Product Description: Novak's Mod 1 Pinion Gears (#5115 / 21T, #5116 / 22T, #5117 / 23T) feature a high-strength hardened steel construction and are precision machined. These gears are compatible with Novak’s Ballistic 8, Ballistic 550, and other motors with a 5mm output shaft. Each gear includes a set screw.