Dealer says 1/2 in.-13 x 5/8 in. button head bolts and Gardner Wescoot website says the same thing. I just called my guy Dan at Topline Fasteners and ordered some 12 point polished ss to match the rest of the bolts on my bike. He has the button head polished ss bolts as well if anyone needs them. I think he said $2.55?? I went the chrome route once and got tired of rust in the allen heads. I went to the polished ss and they look great...looks like chrome and no rust!