These are Replacement Gears and Shafts for the Traxxas EZ-Start System. Steel main gear.Nylon and nylon/metal gears.Metal gear shafts.Includes: One 29T Steel Main Gear; One 18T x 10T Nylon/Metal Gear; One 37T x 11T Nylon Gear; Two 3 x 14mm Metal Shafts; One 3 x 5mm Brass Bushing.Requires: Traxxas vehicle with EZ-Start system.