Which is stronger, 8.8 or grade 5?

Understanding Bolt Strength: Grade 5 vs. Class 8.8

When it comes to fasteners, one of the most common questions is: Which is stronger—Grade 5 or metric Class 8.8? The answer might surprise you—both are roughly equivalent in tensile strength, meaning they can withstand similar levels of pulling force before breaking.

Tensile strength is the maximum stress a bolt can handle before it fractures. While Grade 5 (an SAE standard commonly used in the U.S.) and Class 8.8 (its metric counterpart) come from different classification systems, their performance is closely matched. This parallel also holds true between Grade 8 and Class 10.9 bolts, which are similarly aligned in strength.

However, strength isn’t just about when a bolt snaps. Yield strength is just as important—it’s the point at which a bolt stretches permanently and can no longer return to its original shape. Both Grade 5 and Class 8.8 bolts are engineered to deform before failing completely, providing a safety margin in critical applications.

Choosing between them often comes down to regional standards, availability, or specific project requirements rather than raw strength. In practice, you can often substitute one for the other—provided the thread size, pitch, and length match and the application isn’t extremely high-stress or safety-critical.

Ultimately, understanding these ratings helps ensure the right bolt is chosen for durability and safety. Whether you're working with SAE grades or metric classes, knowing that Grade 5 ≈ Class 8.8—and Grade 8 ≈ Class 10.9—simplifies decision-making in workshops and industrial settings alike.