Grade 8 Hex Cap Screws are manufactured from medium carbon alloy steel. In diameters 1/4 to 1 1/2 inches our Grade 8 material meets or exceeds SAE J429 Grade 8 specifications. Diameters over 1 1/2 inches meet or exceed ASTM A354 Grade BD. All material is manufactured with rolled threads. Yellow zinc plated bolting will meet or exceed ASTM F1941. Typical hardness on diameters 1/4 to 2 1/2 inches is HRC 33-39. On diameters over 2 1/2 inches, hardness will range from HRC 31-39. Tensile strength on diameters 1/4 to 2 1/2 inches is a minimum of 150,000 psi. Diameters over 2 1/2 inches have a meet a minimum of 140,000 psi.Porteous Fastener Company