Grade 5 Carriage Bolts are manufactured from medium carbon steel. Our Grade 5 material meets or exceeds SAE J429 Grade 5 specifications and is manufactured with rolled threads. Zinc plated material meets or exceeds ASTM F1941. Typical hardness on diameters of 1/4 to 1 inch is HRC 25-34. Tensile strength on diameters 1/4 to 1 inch will meet a minimum of 120,000 psi.Brighton-Best International