ARP 612-1000 5/16-18 x 1.000 12pt SS bolts Bolts have a diameter of 5/16", a standard thread pitch of 18, an under head length of 1.000, and the wrenching is 3/8 Rated at 170,000 PSI, which is considerably stronger than Grade 8 hardware Manufactured from polished Stainless 300 steel, a proprietary alloy that is impervious to rust and corrosion