These are Traxxas 32 Pitch Hardened Steel Pinion Gears. These gears are used for various Traxxas models and feature 5mm Bore center hole, compatible with 5mm motor shafts.
For: Traxxas Hoss
Traxxas 32P 11T Hardened Steel Pinion Gear (1 pc)
5mm Bore (1 pc)