This is the optional Robinson Racing 12 Tooth Pinion Gear for the Traxxas Revo 2.5, 3.3, and T-Maxx 3.3. FEATURES: Extra hardened steel construction for durability Precision made For use in extreme conditions INCLUDES: One 12 tooth pinion gear One 4x4mm set screw REQUIRES: Installation onto the motor shaft SPECS: Length: .48" (12.15mm) Mounting hole diameter: 5mm COMMENTS: Also available is a: 13 tooth pinion RRPC1213 14 tooth pinion RRPC1214 15 tooth pinion RRPC1215 17 tooth pinion RRPC1217 18 tooth pinion RRPC1218 19 tooth pinion RRPC1219 cnh 04/12/08 ir/jxs