Marking Requirements on Nuts
| Grade | Required marking |
|---|---|
| O, A, B | No marking required |
| C | Manufacturers ID plus 3 circumferential lines 120 apart |
| C3 | Manufacturers ID plus 3 circumferential lines 120 apart plus numeral 3 |
| D | Manufacturers ID plus D |
| DH | Manufacturers ID plus DH |
| DH3 | Manufacturers ID plus DH-3 if heavy hex, HX3 if standard hex |