Bolt Grades Explained: 4.6, 8.8, 10.9, 12.9 and Stainless A2/A4

Every structural bolt carries its grade stamped on the head. Learn to read it and you can match the right fastener to the load without guessing.

Carbon steel: the dot-number system

Grades like 4.6, 8.8, 10.9 and 12.9 describe strength. The first number relates to tensile strength, the second to yield as a fraction of it. In practice: 4.6 is mild-steel general-purpose; 8.8 is the workhorse structural grade for most steelwork; 10.9 and 12.9 are high-tensile grades for heavily loaded or high-precision connections.

Higher grade means higher strength but also less ductility, so more grade is not automatically better, match it to the design.

Stainless: A2 and A4

Stainless fasteners use a different code. A2 corresponds broadly to SS 304, A4 to SS 316. The trailing number (A2-70, A4-80) indicates strength. Choose A2 for general corrosion resistance and A4 for coastal, marine and chemical exposure, the same 304-versus-316 logic that governs the Gulf's salt air.

Getting it right on site

If your drawings call a grade, match it exactly, mixing grades in a connection undermines the design. We carry the full range in GI, mild and stainless from our Deira counter; send your fastener schedule for a same-day quote.