This bolt has a .560 diameter flange and a 5/16 12 point head. ARP 300 grade 8 stainless bolts, studs, and nuts are virtually impervious to rust and corrosion. Rated at 170,000 psi makes these stronger than regular grade 8 fasteners. These are maintenance free fasteners and come with a polished finish. These bolts have a .560 flange diameter.