Novak 5121 Mod 1 Hardened Steel Pinion Gear, 5mm, 3-Pack (12T, 13T and 14T) Five different combinations are offered of these hardened gears, allowing drivers to experiment with gear ratios These are the same high-quality gears offered individually, but in a money-saving combo pack Novak's Mod 1 Pinion Gears feature a high-strength hardened steel construction and are precision machined These gears are compatible with Novaks Ballistic 8, Ballistic 550, and other motors with a 5mm output shaft Each gear includes a set screw