ARP 4001110 Stainless 300 Hex Header Bolt Kit - Pack of 16 1.00 Inch Length; Hex Style Head Type Smaller Hex Head uses 5/16 inch Wrench The Stainless 300 Material Is Not Affected By Corrosion Or Extreme Heat, Making It Ideal For The Application Nominally Rated At 180,000 PSI Tensile Strength 3/8-16 Inch Thread Size