[Overdriven]

Stock gears are 32 pitch. 68t spur is stock, 65t and 63t are optional, but the 63t won't work without a big pinion due to the motor hitting the trans. Nitro Revo spurs will bolt on the stock slipper and are Mod 1. But the biggest is 40t and I'm pretty sure that's way too small to use. I'm sure there are other mod 1 gears you could use, but I'm not aware of any myself.

Edit: just realize you only needed to know what "pitch pinion" not what pinion size.