Determining Bolt Grades & Understanding Head Markings
The Nut and Bolt Solution Series
Identifying bolt grades and head markings for US grades 2, 5 and 8. Metric grades 8.8.,10.9 and 12.9 (socket products).
Video 1: Determining Bolt Grade and Head Markings
| Grade | Radial Bolt Markings | Material | Nominal Size Diameter/Inches | Proof
Load psi |
Tensile
Strength minimum psi |
Yield
Strength minimum psi |
| Grade 2 No Radial Lines |
 |
Low or Medium Carbon Steel | 1/4" to 3/4" | 55,000 | 74,000 | 57,000 |
| Over 3/4" thru 1 1/2" | 33,000 | 60,000 | 36,000 | |||
| Grade 5 3 Radial Lines |
 |
Medium Carbon Steel | 1/4" to 1" | 85,000 | 120,000 | 92,000 |
| Over 1" thru 1 1/2" | 74,000 | 105,000 | 81,000 | |||
| Grade 8 6 Radial Lines |
 |
Medium Carbon Alloy Steel | 1/4" thru 1 1/2" | 120,000 | 150,000 | 130,000 |
| Metric 8.8 |  |
Medium Carbon Steel | All sizes under 16mm | 580 | 800 | 640 |
| 16mm thru 72mm | 600 | 830 | 660 | |||
| Metric 10.9 |  |
Alloy Steel | 5mm thru 100mm | 830 | 1040 | 940 |
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