This is the Castle Creations 16T 32P Pinion Gear. FEATURES: Aluminum construction For use on monster trucks INCLUDES: One 16T 32P Pinion Gear One 4x4mm Set Screw REQUIRES: Installation on the vehicle SPECS: Length: 12mm (0.47") Inner Diameter: 5mm (0.20") Castle CreationsPart CSE010-0065-00