Gotta have a way to get the power from the motor to the drivetrain. Sounds like the worlds supply of 5mm pinions evaporated once the Mamba Monster came out. Machined from aluminum. Most common uses will be for monster trucks.
28T Aluminum pinion for Monster Trucks
32 Pitch
5 mm shaft hole
Available in 16T, 18T, 20T, 22T, 24T, 26T and 28T.