5/16-18 Grade 2 Finished Hex Nut HDG – Grade 2 Finished Hex Nuts are manufactured from low carbon steel, 1008-1010 for diameters up to 1 inch (cold-formed) and 1045 steel for diameters over 1 inch (hot-formed). Material is manufactured to meet or exceed ASTM A563 Grade A. Zinc plated material will meet or exceed ASTM F1941. Hot-Dip Galvanized material will meet or exceed ASTM A563. Hot-Dip Galvanized nuts are over tapped per ASTM A563. Hardness requirements of HRB 68 – HRC 32 are met or exceeded. Proof load strength of 90,000 psi minimum is met for plain or zinc plated material, 68,000 psi for Hot-Dip Galvanized material.