Product Description: This is Novak's 5mm Mod 1 Steel Pinion Gear 3-Pack (21T/22T/23T). These hardened gears are available in packs of three 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 Novak’s Ballistic 8, Ballistic 550, and other motors with a 5mm output shaft. Each gear includes a set screw.