Bolt Grade Markings and Strength Chart
US Bolts |
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| Head Marking |
Grade and Material |
Nominal Size Range (inches) |
Mechanical Properties | ||
|---|---|---|---|---|---|
|
Proof Load (psi) |
Min. Yield Strength (psi) |
Min. Tensile Strength (psi) |
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 |
307ALow carbon steel |
1/4" thru 4" | N/A | N/A | 60,000 |
 No Markings |
Grade 2Low or medium carbon steel |
1/4" thru 3/4" | 55,000 | 57,000 | 74,000 |
| Over 3/4" thru 1-1/2" | 33,000 | 36,000 | 60,000 | ||
 3 Radial Lines |
Grade 5Medium carbon steel, quenched and tempered |
1/4" thru 1" | 85,000 | 92,000 | 120,000 |
| Over 1" thru 1-1/2" | 74,000 | 81,000 | 105,000 | ||
 6 Radial Lines |
Grade 8Medium carbon alloy steel, quenched and tempered |
1/4" thru 1-1/2" | 120,000 | 130,000 | 150,000 |
|
Grade A325Carbon or alloy steel with or without boron |
1/2" thru 1-1/2" | 85,000 | 92,000 | 120,000 |
| Stainless Markings Vary |
18-8 & 316 StainlessSteel alloy with chromium and nickel |
All sizes thru 1" | N/A | 20,000 Min. 65,000 Typical | 65,000 Min. 100,000 – 150,000 Typical |
 |
651 Silicon bronzeAn alloy of mostly copper and tin with a small amount of silicon |
1/4" thru 3/4" | N/A | 55,000 | 70,000 |
| 7/8" thru 1-1/2" | N/A | 40,000 | 55,000 | ||
 |
Aluminum 2024Aluminum alloy with copper, magnesium and manganese; solution heat treated and age hardened |
All sizes | N/A | 36,000 | 55,000 |
Metric Bolts |
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| Head Marking |
Class and Material |
Nominal Size Range (mm) |
Mechanical Properties | ||
|
Proof Load (MPa) |
Min. Yield Strength (MPa) |
Min. Tensile Strength (MPa) |
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|
Class 8.8Medium carbon steel, quenched and tempered |
All sizes below 16mm | 580 |
640 |
800 |
| 16mm - 72mm | 600 | 660 | 830 | ||
|
Class 10.9Alloy steel, quenched and tempered |
5mm - 100mm | 830 |
940 |
1040 |
|
Class 12.9Alloy steel, quenched and tempered |
1.6mm - 100mm | 970 |
1100 |
1220 |
| Usually Stamped A-2 or A-4 |
A-2 & A-4 StainlessSteel alloy with chromium and nickel |
All sizes thru 20mm | N/A |
210 Min. |
500 Min. |
|
Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing. Yield Strength: The maximum load at which a material exhibits a specific permanent deformation. Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set. 1MPa = 1N/mm2 = 145 pounds/inch2 |
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