Complete Torque Chart for SAE Grade 8 Fasteners
Grade 8 Bolt Torque Chart
Complete torque specifications for SAE Grade 8 fasteners — the highest strength commonly available commercial fasteners for critical and high-stress applications.
Grade 8 bolts deliver 25% more clamping force than Grade 5 at the same size. These torque values are calculated at 75% of proof load. Always follow engineering specifications for critical applications.
SAE Grade 8 Specifications
Medium Carbon Alloy Steel, Quenched & Tempered — ASTM A354 Grade BD
UNC (Coarse Thread) Torque Specifications
| Size | TPI | Dry Torque (ft-lbs) |
Dry Torque (Nm) |
Lubricated (ft-lbs) |
Lubricated (Nm) |
Clamp Load (lbs) |
|---|---|---|---|---|---|---|
| #6 | 32 | 2.0 | 2.7 | 1.5 | 2.0 | 400 |
| #8 | 32 | 3.8 | 5.2 | 2.9 | 3.9 | 630 |
| #10 | 24 | 5.6 | 7.6 | 4.2 | 5.7 | 890 |
| 1/4" | 20 | 12 | 16 | 9 | 12 | 2,400 |
| 5/16" | 18 | 24 | 33 | 18 | 24 | 3,850 |
| 3/8" | 16 | 44 | 60 | 33 | 45 | 5,650 |
| 7/16" | 14 | 70 | 95 | 53 | 72 | 7,750 |
| 1/2" | 13 | 105 | 142 | 79 | 107 | 10,350 |
| 9/16" | 12 | 155 | 210 | 116 | 157 | 13,250 |
| 5/8" | 11 | 210 | 285 | 158 | 214 | 16,500 |
| 3/4" | 10 | 375 | 508 | 281 | 381 | 24,500 |
| 7/8" | 9 | 605 | 820 | 454 | 616 | 33,800 |
| 1" | 8 | 910 | 1,234 | 683 | 926 | 44,000 |
| 1-1/8" | 7 | 1,280 | 1,736 | 960 | 1,302 | 55,500 |
| 1-1/4" | 7 | 1,820 | 2,468 | 1,365 | 1,851 | 70,000 |
| 1-3/8" | 6 | 2,380 | 3,227 | 1,785 | 2,421 | 83,000 |
| 1-1/2" | 6 | 3,160 | 4,285 | 2,370 | 3,214 | 101,000 |
UNF (Fine Thread) Torque Specifications
💡 Fine Thread Advantage
Fine thread Grade 8 fasteners provide approximately 10-15% higher torque capacity due to increased tensile stress area. Ideal for precision assemblies requiring maximum clamping force.
| Size | TPI | Dry Torque (ft-lbs) |
Dry Torque (Nm) |
Lubricated (ft-lbs) |
Lubricated (Nm) |
Clamp Load (lbs) |
|---|---|---|---|---|---|---|
| #6 | 40 | 2.3 | 3.1 | 1.7 | 2.3 | 450 |
| #8 | 36 | 4.2 | 5.7 | 3.2 | 4.3 | 700 |
| #10 | 32 | 6.3 | 8.5 | 4.7 | 6.4 | 1,000 |
| 1/4" | 28 | 13 | 18 | 10 | 14 | 2,700 |
| 5/16" | 24 | 27 | 37 | 20 | 27 | 4,300 |
| 3/8" | 24 | 49 | 66 | 37 | 50 | 6,350 |
| 7/16" | 20 | 78 | 106 | 59 | 80 | 8,700 |
| 1/2" | 20 | 117 | 159 | 88 | 119 | 11,650 |
| 9/16" | 18 | 170 | 230 | 128 | 174 | 14,850 |
| 5/8" | 18 | 238 | 323 | 179 | 243 | 18,600 |
| 3/4" | 16 | 420 | 569 | 315 | 427 | 27,400 |
| 7/8" | 14 | 670 | 908 | 503 | 682 | 37,800 |
| 1" | 12 | 1,010 | 1,370 | 758 | 1,028 | 49,200 |
| 1-1/8" | 12 | 1,440 | 1,953 | 1,080 | 1,465 | 62,500 |
| 1-1/4" | 12 | 2,040 | 2,766 | 1,530 | 2,075 | 78,500 |
| 1-3/8" | 12 | 2,680 | 3,634 | 2,010 | 2,726 | 94,000 |
| 1-1/2" | 12 | 3,560 | 4,828 | 2,670 | 3,621 | 114,000 |
Important Considerations
🚨 Hydrogen Embrittlement Risk
Grade 8 bolts (HRC 33+) are susceptible to hydrogen embrittlement when electroplated. For zinc-plated Grade 8 fasteners, ensure proper baking (375°F for 4+ hours) was performed after plating. Consider mechanical galvanizing as an alternative.
⚠️ Lubrication Warning
Using dry torque values on lubricated fasteners can result in over-tightening by up to 25%, potentially causing bolt failure. Always verify lubrication condition before selecting torque values.
🔧 Grade 8 vs. Grade 5
Grade 8 provides 25% higher tensile strength than Grade 5. However, this extra strength means Grade 8 is less ductile (more brittle). For applications with vibration or shock loading, ensure proper lockwashers or thread locking compound are used.
Grade 8 Applications
Where to Use Grade 8 Bolts
- Automotive: Engine mounts, transmission mounts, suspension pivots, drivetrain
- Heavy equipment: Loader arms, excavator attachments, lifting hardware
- Industrial: Press frames, die plates, high-stress machinery
- Structural: Bridge connections, crane attachments, steel erection
- Agricultural: Implement hitches, PTO shafts, heavy-duty brackets
When NOT to Use Grade 8
Avoid Grade 8 for applications where some ductility is beneficial (preventing sudden failure), corrosive environments without proper coating protection, or where the mating material cannot handle the higher clamping force.
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