Gear, 14-T pinion (0.8 metric pitch, compatible with 32-pitch) / set screw. Optional Traxxas pinion gears allow you to increase or decrease the final drive ratio and tune for different applications. Larger gears will result in higher speeds while smaller gears provide more torque. These are designed for use with 32-pitch spur gears and 5mm motor shafts.
This is the 5640 Gear 32P 14T Hardened Steel 5mm Shaft/Set Screw from Traxxas. Traxxas has grown to become the number-1 selling name in RTR nitro and electric models for the last 4 years running. No one has done more than Traxxas to advance the RTR category with innovative thinking and fun designs that make it easy for anyone to get started in the great R/C hobby. Traxxas, truely the fastest name in Radio Control!