Grade 8 Fasteners vs Alloy Steel - Is there a difference?

Grade 8 screws are equivalent to metric grade 10.9. Alloy steel socket head screws (ASTM A574) are stronger than grade 8 screws and are equivalent to metric grade 12.9.

Alloy steel is the most common grade in socket head cap screws. These socket heads are also commonly manufactured with a 3A thread fit – tighter and more precise than the 2A fit on most grade 5 or grade 8 fasteners. They are often used in blind holes in precisely machined equipment. Where grade 8’s might be removed as part of regular maintenance, socket heads are meant to resist loosening and hold strength for a longer maintenance cycle – often the entire lifecycle of the equipment.