build a gmaxx and i need help

[suicideneil]

With a plastic spur you can use pretty much any pinion material, though the harder the material the longer it will last ( I've seen aluminium pinions worn down by nylon spur gears quite baddly ).

If you use the ofna steel spurs, then a hardend steel pinion is the best choice- one of Mike's or a RobinsonRacing being the most popular ones Im familar with.