Good quality 32 pitch 3mm aluminium pinion gears in the most common sizes.

Terminology
Pinion: The smaller gear which goes on the motor.
Spur Gear: The larger gear which goes on the gearbox or drivetrain.

Sizing
32 Pitch: The gap between each tooth, check this matches your spur gear.
3mm: The size of the hole, check this matches your motor shaft.

Gearing
Smaller Pinion/Larger Spur gear: Lower top speed, higher acceleration, lower motor temperature.
Larger Pinion/Smaller Spur gear: Higher top speed, lower acceleration, higher motor temperature.
-Motors may be geared according to desired performance, maximum gearing must be determined according to motor temperature.
-A safe maximum of 65c under worst case conditions is recommended to avoid motor damage.
-Conditions that may contribute to the highest motor temperature include: high ambient temperature, high tyre grip,
heavy and repeated acceleration and breaking, off road environments particularly grass and mud.

Installation
-Gear mesh must be set correctly to avoid damage particularly to plastic spur gears. There must be a small gap in the mesh between each gear.
The gap should be just enough that the gears run smoothly and play can be felt when moving either gear by hand.
-Low strength thread-lock must be used on the grub screw. Use heat from a soldering iron to deactivate threadlock before removal.
-Use of Hex-Plus bits/drivers to avoid stripping out grub screws is recommended.
-Where a grub screw strips out, remove motor and use a punch to gently and slowly hammer out motor shaft whilst supporting pinion in a vice.

Notes
-Appearance may vary from picture, does not affect functionality.
-If the size you require isn't listed, consider changing your spur gear to allow use of a more common size.
-Requires modification to fit the traxxas trx-4 due to limited clearance.