The nut that holds the clutch nut on a Genesis is actually a 17 or 19mm. I can't remember off the top of my head. And yes I am sure it's a 17mm or 19mm. It's a huge clutch, what do you expect?? LOL

10mm is the standard size clutch nut for most 8th scales, but not the GST/Genesis/Nemesis. hahaha