Just make sure you need them!!!

Some gearboxes are different then others and not all of them need these shims. Check the manual it explains how to get it just right and how much play you should have between the gears.

The quality of HPI is not as good as say Losi or Team Associated there for you get inconsistencies with their products. The designed of the gearboxes sucks to begin with I wish HPI would address this issues instead of banddading it by providing shims. I am going to get the aluminum gear box cases one of these days and then I will not have to deal with this dam problem anymore.