1/8 scale cars generally run Mod1 gears, 1/10 scale trucks runs Mod .8, generally referred to as "32 pitch gears", and some smaller 1/10 cars even run 48 pitch gears
It's just a way to measure the size of gear teeth and make sure you have proper gears on custom builds
_______________________________________
It's "Dr. _paralyzed_" actually. Not like with a PhD, but Doctor like in Dr. Pepper.