This chart helps to identify the grades of bolts using the identification marks on the bolt's head along with the strength and hardness of common grade bolts. Please note the bolt heads may also include the manufacturer's identification stamp, especially with high strength bolts.
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Bolt Grade Markings & Strength Chart - Inch Steel Bolts |
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Head Marking |
Bolt Grade / Specification |
Material |
Nominal Size (Inch) |
Proof Load psi |
Tensile Strength Min psi |
Yield Strength Min psi |
Rockwell Hardness Min/Max |
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Grade 1 - SAE J429 Bolts, Screws and Studs |
Low or medium carbon steel | 1/4" - 1-1/2" | 33,000 | 60,000 | 36,000 | B70 / B100 |
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Grade 2 - SAE J429 Bolts, Screws and Studs |
Low or medium carbon steel |
1/4" - 3/4" >3/4" - 1-1/2" |
55,000 33,000 |
74,000 60,000 |
57,000 36,000 |
B80 / B100 B70 / B100 |
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Grade 5 - SAE J429 Bolts, Screws and Studs |
Medium carbon steel or carbon steel with additives, quenched and tempered |
1/4" - 1" >1" - 1-1/2" |
85,000 74,000 |
120,000 105,000 |
92,000 81,000 |
C25 / C34 C19 / C30 |
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Grade 5.1 - SAE J429 Sems |
Low or medium carbon steel, quenched and tempered |
No. 4 - 5/8" |
85,000 |
120,000 |
92,000 |
C25 / C40 |
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Grade 5.2 - SAE J429 Bolts, Screws and Studs |
Low carbon Boron steel, quenched and tempered |
1/4" - 1" |
85,000 |
120,000 |
92,000 |
C26 / C36 |
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Grade 8 - SAE J429 Bolts and Screws |
Medium carbon / alloy steel with additives, quenched and tempered |
1/4" - 1-1/2" |
120,000 |
150,000 |
130,000 |
C33 / C39 |
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Grade 8.2 - SAE J429 Bolts and Screws |
Low carbon Boron steel, quenched and tempered |
1/4" - 1" |
120,000 |
150,000 |
130,000 |
C33 / C39 |
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L9 - Grade 9 Bolts, Nuts and Washers |
Hight strength alloy steel |
1/4" - 1-1/2" |
145,000 |
180,000 |
155,000 |
C38 / C42 |
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ASTM A307 Grade A Bolts, Screws and Studs (General Engineering) |
Low or medium carbon steel |
1/4" - 4" |
33,000 |
60,000 |
36,000 |
B69 / B100 |
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ASTM A307 Grade B Bolts, Screws and Studs (Flanged Joints) |
Low or medium carbon steel |
1/4" - 4" |
33,000 |
60,000 |
36,000 |
B69 / B95 |
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ASTM A325 Type 1 High strength structural bolts |
Medium carbon steel, quenched and tempered |
1/2" - 1" 1-1/8" - 1-1/2" |
85,000 74,000 |
120,000 105,000 |
92,000 81,000 |
C24 / C35 C19 / C31 |
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ASTM A325 Type 2 High strength structural bolts |
Low carbon Martensitic steel, quenched and tempered |
1/2" - 1" 1-1/8" - 1-1/2" |
85,000 74,000 |
120,000 105,000 |
92,000 81,000 |
C24 / C35 C19 / C31 |
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ASTM A325 Type 3 High strength structural bolts |
Atmospheric corrosion-resistant steel, quenched and tempered |
1/2" - 1" 1-1/8" - 1-1/2" |
85,000 74,000 |
120,000 105,000 |
92,000 81,000 |
C24 / C35 C19 / C31 |
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ASTM A354 Grade BB Bolts and studs |
Alloy steel, quenched and tempered |
1/4" - 2-1/2" > 2-1/2" - 4" |
80,000 75,000 |
105,000 100,000 |
83,000 78,000 |
C26 / C36 C22 / C33 |
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ASTM A354 Grade BC Bolts and studs |
Alloy steel, quenched and tempered |
1/4" - 2-1/2" > 2-1/2" - 4" |
105,000 95,000 |
125,000 115,000 |
109,000 99,000 |
C26 / C36 C22 / C33 |
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ASTM A354 Grade BD Bolts, screws and studs |
Alloy steel, quenched and tempered |
1/4" - 2-1/2" > 2-1/2" - 4" |
120,000 105,000 |
150,000 140,000 |
130,000 120,000 |
C33 / C39 C31 / C39 |
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ASTM A449 Type 1 Bolts, screws and studs |
Medium carbon steel, quenched and tempered |
1/4" - 1" >1 - 1-1/2" |
85,000 74,000 |
120,000 105,000 |
81,000 58,000 |
C25 / C34 C19 / C30 |
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ASTM A449 Type 2 Bolts, Screws and studs |
Low carbon Martensitic steel, quenched and tempered |
1/4" - 1" |
85,000 |
120,000 |
58,000 |
C25 / C34 |
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ASTM A490 Type 1 High strength structural bolts |
Medium carbon alloy steel, quenched and tempered |
1/2" - 1-1/2" |
120,000 |
150,000 min 170,000 max |
130,000 |
C33 / C38 |
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ASTM A490 Type 2 High strength structural bolts |
Low carbon Martensitic steel, quenched and tempered |
1/2" - 1" |
120,000 |
150,000 min 170,000 max |
130,000 |
C33 / C38 |
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ASTM A490 Type 3 High strength structural bolts |
Atmospheric corrosion-resistant steel, quenched and tempered |
1/2" - 1-1/2" |
120,000 |
150,000 min 170,000 max |
130,000 |
C33 / C38 |
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Note: Manufacturer's identification mark are also stamped when applicable. |
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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
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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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Tensile Strength: The resistance of a material to breaking under tension
Yield Strength: The stress at which a specific amount of deformation is produced
Proof Load: An axial tensile load which the product must stand without evidence of any permanent set.
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