The "Pro" Pinions are precision machined from 7075 grade aluminum and anodized with a super hard jet black finish that not just hardends the surface but also protects the gear from corrosion and increases the lubricity by reducing friction and adhesion between the pinion gear and spur gear.
Recommended for onroad, but they can be run off road. A wide selection of tooth sizes are available. Tooth number stamped on each pinion. 1/8 inch (3.17mm) bore. One 5-40 set screw included.
The pinion itself seems to be of solid quality and I wish I could have used it.
Figured I might save someone the expense of finding out it won't work for the Axial 55T motor (AX24007).