ARP Chromoly Header Bolt Kits 100-1110. Header Bolts, Hex Head, 5/16 in. Wrench, Steel, Black Oxide, 3/8 in.-16, 1.00 in. U.H.L., Set 16. ARP Chromoly Header Bolt Kits. ARP manufactures a variety of header bolt kits to facilitate the installation of your headers.