Jul 2025
Bolt Grade Markings and Strength Chart
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Bolt Grade Markings & Strength Chart - Metric Steel Bolts
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| Head Marking |
Grade/Specification |
Material |
Proof Load (MPa) |
Tensile Strength min (MPa) |
Yield Strength Min (MPa) |
Hardness Min/Max |
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Class 4.6 |
Low or medium carbon steel |
220 |
400 (58,000 psi) |
240 |
HRB-67 / HRB-95 |
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Class 5.8 |
Low or medium carbon steel, quenched and tempered |
380 |
520 (75,000 psi) |
420 |
HRB-82 / HRB-95 |
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Class 8.8 |
Medium carbon steel, quenched and tempered |
600 |
830 (120,000 psi) |
640 |
HRC-22 / HRC-34 |
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Class 10.9 |
Alloy steel, quenched and tempered |
830 |
1040 (150,000 psi) |
940 |
HRC-32 / HRC-39 |
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Class 12.9 |
Alloy steel, quenched and tempered |
970 |
1220 (176,000 psi) |
1220 |
HRC-39 / HRC-44 |
| Usually stamped A-2 or A-4 |
A2 & A4 Stainless |
Steel alloy with chromium and nickel |
N/A |
500 Min
700 Typical |
210 Min
450 Typical |
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Note: Manufacturer's identification mark are also stamped when applicable.
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Bolt Grade Markings & Strength Chart - Inch Steel Bolts
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| Head Marking |
Grade / Specification |
Material | Size (Inch)
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Proof Load (psi) |
Tensile Strength Min (psi) |
Yield Strength Min (psi) |
Rockwell Hardness |
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Grade 1 - SAE J429
Bolts, Screws and Studs |
Low/Medium Carbon Steel |
1/4" - 1-1/2" |
33,000 |
60,000 |
36,000 |
HRB 70 / HRB 100 |
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Grade 2 - SAE J429
Bolts, Screws and Studs |
Low/Medium Carbon Steel |
1/4" - 3/4"
>3/4" - 1-1/2" |
55,000
33,000 |
74,000
60,000 |
57,000
36,000 |
HRB 80 / HRB 100
HRB 70 / HRB 100 |
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Grade 5 - SAE J429
Bolts, Screws and Studs |
Medium Carbon Steel, Quenched & Tempered |
1/4" - 1"
>1" - 1-1/2" |
85,000
74,000 |
120,000
105,000 |
92,000
81,000 |
HRC 25 / HRC 34
HRC 19 / HRC 30 |
| Grade 5.1 - SAE J429 |
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Note: Manufacturer's identification marks are also stamped where applicable. Data as per SAE J429 & ASTM standards.
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