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
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| 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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Our disclaimer: 24 years as a fastener distributor may make us knowledgeable and familiar with common fastener questions. It doesn't qualify us as technical experts. We will gladly refer you to the fastener industries "authorities" for your technical specifications. NFDA - The National Fasteners Distributors Association. IFI - Industrial Fasteners Institute. STAFDA - Specialty Tools and Fasteners Distributors Association
