Over 1/2 of of mine had the heads broken off of them in all 8 of the stand off brackets. The dealer replaced each and everyone of them under warranty. Sorry but I don't know what the size was.
I took pictures of mine and plan on asking the factory bubbas in August at the rally why they don't use stainless. I have pictures of stainless steel screws from lowes that show a cost difference of a few cents, and that's at retail.