Glossary

A Grade 8 fastener is a high-strength, high-performance bolt or screw made from medium-carbon alloy steel and heat-treated to achieve some of the highest mechanical properties in the SAE J429 grading system. Grade 8 bolts are significantly stronger than both Grade 2 and Grade 5 and are used whenever the joint must withstand high loads, shock, vibration, or critical structural forces.

Grade 8 fasteners are typically manufactured from steels such as medium-carbon alloy (like 4037 or 4140) and are quenched and tempered to achieve very high hardness and tensile strength. Their minimum tensile strength is approximately 150,000 psi, and their yield strength is around 130,000 psi, making them one of the strongest readily available standard inch-series bolt grades.

In practical industrial settings, these fasteners are used in heavy equipment, automotive suspensions, engine assemblies, agricultural machinery, off-highway vehicles, structural support systems, hydraulic components, and any application where failure would be dangerous or costly. They handle high clamping force, resist deformation under heavy loads, and hold up well in dynamic or vibration-prone environments.

Grade 8 hex bolts are easily identified by six radial lines on the head, which is a universal SAE marking. They are usually supplied in yellow zinc, clear zinc, phosphate and oil, or plain finishes depending on corrosion requirements. For customers choosing between grades, Grade 8 is ideal when maximum strength is required, while still being compatible with standard inch-series tooling and thread classes.