Grade 8 Bolts

A Grade 8 bolt is a high-strength, heat-treated steel bolt defined by the SAE J429 standard and commonly used in demanding mechanical joints. Compared to lower grades (like Grade 5), Grade 8 fasteners are designed to handle higher clamp loads and higher tensile stresses, making them a common choice in heavy equipment, automotive suspension and drivetrain assemblies, industrial machinery, and other high-load connections. Grade 8 bolts are typically identified by six radial lines stamped on the head.

Because of their strength, Grade 8 bolts should be paired with the correct matching nuts and washers (and appropriate thread engagement) so the joint can carry load without stripping or embedding. Proper torque is important: under-torquing can allow joint movement and fatigue, while over-torquing can yield the bolt or damage threads. Also note that “Grade 8” is not the same thing as structural bolt grades (like ASTM A325/A490) or metric property classes (like 10.9 or 12.9), so it’s important to match the fastener grade to the drawing/specification and the application requirements.