This is the Mod-1 17T Pinion Gear from Castle Creations. FEATURES: Hardened steel construction Designed for 1/8 scale cars INCLUDES: One Mod-1 17T Pinion Gear One 4x4mm Set Screw SPECS: Outer Diameter: 19mm (0.75") Inner Diameter: 5mm (0.20") Width: 12mm (0.47") Castle CreationsPart CSE010-0065-10