These bolts are equivalent to Metric grade 10.9. They have a 12 point flanged head with a 18mm flange diameter. Use a 12mm 12 point wrench or socket to install. ARP 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.