Bolt Comparison Chart
Bolt Grade & Class Comparison Chart
Compare mechanical properties across SAE, ASTM, and Metric (ISO) bolt grades. Understand tensile strength, proof load, hardness, and head markings to select the right fastener for your application.
SAE Bolt Grades — J429
| Grade | Material | Tensile Strength PSI (min) | Proof Load PSI | Yield Strength PSI (min) | Hardness Rockwell | Head Marking |
|---|---|---|---|---|---|---|
| Grade 2 | Low/Medium Carbon Steel | 74,000 | 55,000 | 57,000 | B70–B100 | No lines |
| Grade 5 | Medium Carbon Steel, Q&T | 120,000 | 85,000 | 92,000 | C25–C34 | 3 radial lines |
| Grade 8 | Medium Carbon Alloy, Q&T | 150,000 | 120,000 | 130,000 | C33–C39 | 6 radial lines |
| Grade 8.2 | Low Carbon Martensite Steel | 150,000 | 120,000 | 130,000 | C33–C39 | 8.2 on head |
ASTM Structural Bolt Grades
| Specification | Material | Tensile Strength PSI (min) | Proof Load PSI | Size Range | Head Marking |
|---|---|---|---|---|---|
| A307 Grade A | Low Carbon Steel | 60,000 | — | 1/4"–4" | No marking |
| A325 Type 1 | Medium Carbon Steel, Q&T | 120,000 | 85,000 | 1/2"–1-1/2" | A325 |
| A490 Type 1 | Alloy Steel, Q&T | 150,000 | 120,000 | 1/2"–1-1/2" | A490 |
| F1852 | Twist-Off Type (TC Bolt) | 120,000 | 85,000 | 1/2"–1" | A325 + TC |
| A354 Grade BD | Alloy Steel, Q&T | 150,000 | 120,000 | 1/4"–4" | BD |
Metric Property Classes — ISO 898-1
| Class | Material | Tensile Strength MPa (min) | Proof Load MPa | Yield Strength MPa (min) | SAE Equivalent | Head Marking |
|---|---|---|---|---|---|---|
| Class 4.6 | Low/Medium Carbon | 400 | 225 | 240 | Grade 2 | 4.6 |
| Class 8.8 | Medium Carbon, Q&T | 800 | 580 | 640 | Grade 5 | 8.8 |
| Class 10.9 | Alloy Steel, Q&T | 1,040 | 830 | 940 | Grade 8 | 10.9 |
| Class 12.9 | Alloy Steel, Q&T | 1,220 | 970 | 1,100 | Beyond Gr. 8 | 12.9 |
Stainless Steel Grades
| Alloy | Type | Tensile Strength PSI (min) | Yield Strength PSI (min) | Magnetic? | Corrosion Resistance | Common Uses |
|---|---|---|---|---|---|---|
| 18-8 (304) | Austenitic | 75,000 | 30,000 | Slightly | Excellent | General purpose, food equipment |
| 316 | Austenitic | 75,000 | 30,000 | No | Superior (saltwater) | Marine, chemical, coastal |
| 410 | Martensitic | 110,000 | 85,000 | Yes | Moderate | Heat-treatable applications |
| Silicon Bronze | Copper Alloy | 70,000 | 30,000 | No | Excellent (marine) | Marine, wood boats, electrical |
Understanding Grade Markings
SAE Head Markings
SAE grade bolts are identified by radial lines on the hex head. Grade 2 has no markings. Grade 5 has 3 equally spaced lines. Grade 8 has 6 lines. Always count the lines to verify the grade before installation.
Metric Class Numbers
The first number times 100 gives tensile strength in MPa (e.g., 8.8 = 800 MPa). The decimal represents the yield-to-tensile ratio (e.g., 8.8 means yield is 80% of tensile = 640 MPa). The number is stamped directly on the bolt head.
Q&T = Quenched & Tempered
Higher-grade fasteners (Grade 5+) undergo quenching and tempering — a heat treatment process that increases hardness and strength. This makes them suitable for structural and high-stress applications.
Grade Selection Guidelines
Grade 2: General purpose, non-critical. Grade 5: Automotive, machinery, moderate loads. Grade 8: High-strength, heavy equipment, structural. For corrosion resistance, use stainless or zinc plating. Always consult engineering specs for critical joints.
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