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
Grade 2 Bolt - 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
Grade 5 Bolt - 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
Grade 8 Bolt - 5 Radial Lines Medium Carbon Alloy Steel 1/4" thru 1 1/2" 120,000 150,000 130,000
Metric 8.8 Metric Bolt - Grade 8.8 Medium Carbon Steel All sizes under 16mm 580 800 640
16mm thru 72mm 600 830 660
Metric 10.9 Metric Bolt - Grade 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 InstituteSTAFDA - Specialty Tools and Fasteners Distributors Association

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