This is actually the Differential Ring and Pinion Gear to be used on Traxxas Slash 4x4 automobiles. Features: Steel construction Includes: One Differential Ring Gear One Differential Pinion Gear Specs: Pinion Gear: Enamel: 13T Inner Diameter: 5mm (0.20") Ring Gear: Tooth: 37T Internal Diameter: 6mm (0.24")