Engineering Tools
Reference data for specifying and sourcing fasteners correctly — the numbers a procurement or design engineer actually needs.
Grade markings
How to identify an unmarked or unknown-grade fastener from its head stamp (ISO 898-1 / ISO 3506-1).
| Mark | Meaning | Head appearance |
|---|---|---|
| 4.6 | Property class 4.6 — mild steel, low strength | Plain hex, no radial lines |
| 8.8 | Property class 8.8 — medium carbon steel, quenched & tempered | 3 radial lines from centre |
| 10.9 | Property class 10.9 — alloy steel, quenched & tempered | 4 radial lines from centre |
| 12.9 | Property class 12.9 — alloy steel, high strength | 5 radial lines from centre |
| A2-70 | Austenitic stainless (304-type), strength grade 70 | “A2” or “A2-70” stamped, no radial lines |
| A4-70 / A4-80 | Austenitic stainless (316-type), better corrosion resistance | “A4” stamped |
| Manufacturer logo/code | Traceability mark identifying the maker | Usually alongside the grade mark |