This differential spool replaces the differential gears to make the truck unstoppable in hard-core climbing maneuvers. The spool locks the axle, which in turn provides equal power to both wheels no matter what the truck drives over.

If you're building a radical, special-purpose E-Maxx/T-Maxx for straight-line sand drags, hill climbing or pulling, you can replace both the front and rear differentials with spools for total 4WD traction. For racing the E-Maxx/T-Maxx on tight off-road tracks, install a spool in the rear diff case to allow the rear end of the truck to slide through the corners. The truck will feel loose, but your lap times will go down.