I don't have it yet, but I'd like to be able to put it on as soon as it arrives and not have to bother going to the store and search, so I just thought I'd ask and someone might know off hand.
Well, for future reference, 6mm x 1.0 wingnuts fit perfectly. I almost eyeballed it, but I wasn't looking at metric stuff, so after I tried all the standard sizes, I switched to metric, just walking in and out of the Home Depot to see which ones fit. Installed it in the parking lot just before some rain hit.