Atomik RC Traxxas Slash 4X4 1:16 Performance Speed Tuned Pinion Gear Set, 23T, 28T, 31T Hop Up Upgrade Precision Made and Tuned for Performance. Hardened Steel for Maximum Durability. Easy Upgrade from the Original Part. Includes 23 Tooth, 28 Tooth, and 31 Tooth Pinion Gears. Atomik RC Offers a Full Line of Hop Ups for your Traxxas Slash 4X4 1:16