The chart below organizes bolt grades, their head identification marks, and strength values because knowing how to read them helps you choose hardware that’s right for your job. For example, grade 5 bolt strength is commonly used in general machinery, while grade 8 bolt markings signal a higher tensile rating for heavier-duty assemblies. Metric fasteners follow their own system—bolt strength 10.9 and 12.9 being frequent choices in equipment where shear and tensile demands run higher. Even grade 12 bolts, though less common, appear in specialized high-stress environments.
US Bolts
| Head Marking | Grade and Material | Nominal Size Range (inches) | Proof Load (PSI) | Min. Yield Strength (PSI) | Min. Tensile Strength (PSI) |
|---|---|---|---|---|---|
|
307A
Low-carbon steel, standard grade
|
1/4″ thru 4″ | N/A | N/A | 60,000 | |
|
Grade 2
Low to medium-carbon steel, commercial grade
|
1/4″ thru 3/4″ Over 3/4″ thru 1-1/2″ |
55,000 33,000 |
57,000 36,000 |
74,000 60,000 |
|
|
Grade 5
Heat-treated medium-carbon steel
|
1/4″ thru 1″ Over 1″ thru 1-1/2″ |
85,000 74,000 |
92,000 81,000 |
120,000 105,000 |
|
|
Grade 8
Heat-treated alloy steel, high strength
|
1/4″ thru 1-1/2″ | 120,000 | 130,000 | 150,000 | |
|
Grade A325
Carbon or alloy steel with or without boron
|
1/2″ thru 1-1/2″ | 85,000 | 92,000 | 120,000 | |
|
18-8 & 316 Stainless
Steel alloy with chromium and nickel
|
All sizes thru 1″ | N/A | 30,000 Min 65,000 typical |
65,000 Min 80,000 – 90,000 typical |
|
|
651 Silicon Bronze
Alloy of mostly copper and tin with a small amount of silicon
|
1/4″ thru 3/4″ 7/8″ thru 1-1/2″ |
N/A N/A |
55,000 40,000 |
70,000 55,000 |
|
|
Aluminum 2024
Aluminum alloy with copper, magnesium and manganese; solution heat treated and age hardened
|
All sizes | N/A | 36,000 | 55,000 |
Metric Bolts
| Head Marking | Class and Material | Nominal Size Range (mm) | Proof Load (MPa) | Min. Yield Strength (MPa) | Min. Tensile Strength (MPa) |
|---|---|---|---|---|---|
|
Class 8.8
Heat-treated medium-carbon steel
|
All sizes below 16mm 16mm – 72mm |
580 600 |
640 660 |
800 830 |
|
|
Class 10.9
Heat-treated alloy steel
|
5mm – 100mm | 830 | 940 | 1040 | |
|
Class 12.9
Heat-treated alloy steel, high strength
|
1.6mm – 100mm | 970 | 1100 | 1220 | |
|
A-2 & A-4 Stainless
Stainless steel with chromium and nickel
|
All sizes thru 20mm | N/A | 210 Min. 450 Typical |
500 Min. 700 Typical |
Parting Thoughts
MISUMI USA offers a wide range of screws and bolts—both standard and metric—including hex head bolts, narrow head bolts, square head bolts, and more. If you’re unsure which bolt product best suits your application, our engineering team is here to help. For more technical insights, explore our other manufacturing-focused tables and articles, such as a Metric Bolt Torque Chart.
Author: Scott Bredemann | Updated: 12/11/2025
Disclaimer:
The content on this webpage is for informational purposes only. MISUMI makes no guarantees, expressed or implied, regarding the accuracy, completeness, or validity of the information. Performance parameters, tolerances, designs, materials, or processes should not be assumed to reflect third-party suppliers’ or manufacturers’ deliverables within MISUMI’s network. Buyers are responsible for specifying their part requirements