A563 Grade A Heavy Hex Nuts are manufactured from low carbon steel, 1008-1010 for sizes up to 1 inch (cold-formed) and 1045 steel for sizes 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. Typical hardness is HRB 68 - HRC 32. Proof load strength will meet a minimum of 100,000 psi and 75,000 psi for Hot-Dip Galvanized nuts.Porteous Fastener Company