Screw Torque Reference
Look up recommended torque values by screw size and material.
Covers metric and imperial bolts with common engineering torque specs.
Select bolt system and size — or enter a torque value to convert units.
Proper screw and bolt torque is critical for secure fastening without damaging threads or breaking the fastener. Under-torquing leads to loose joints, while over-torquing can strip threads or snap the bolt.
Torque unit conversions:
- 1 N-m (Newton-meter) = 0.7376 ft-lbs
- 1 ft-lb = 1.3558 N-m
- 1 N-m = 8.851 in-lbs
- 1 ft-lb = 12 in-lbs
Recommended torque for standard metric bolts (Grade 8.8, dry):
| Bolt Size | Pitch (mm) | Torque (N-m) | Torque (ft-lbs) |
|---|---|---|---|
| M4 | 0.7 | 2.9 | 2.1 |
| M5 | 0.8 | 5.8 | 4.3 |
| M6 | 1.0 | 10 | 7.4 |
| M8 | 1.25 | 24 | 17.7 |
| M10 | 1.5 | 47 | 35 |
| M12 | 1.75 | 82 | 60 |
| M14 | 2.0 | 130 | 96 |
| M16 | 2.0 | 200 | 148 |
| M18 | 2.5 | 280 | 207 |
| M20 | 2.5 | 400 | 295 |
| M24 | 3.0 | 690 | 509 |
Recommended torque for imperial bolts (Grade 5, dry):
| Bolt Size | TPI | Torque (ft-lbs) | Torque (N-m) |
|---|---|---|---|
| 1/4"-20 | 20 | 8 | 10.8 |
| 5/16"-18 | 18 | 17 | 23.1 |
| 3/8"-16 | 16 | 31 | 42.0 |
| 7/16"-14 | 14 | 49 | 66.4 |
| 1/2"-13 | 13 | 75 | 101.7 |
| 9/16"-12 | 12 | 110 | 149.1 |
| 5/8"-11 | 11 | 150 | 203.4 |
| 3/4"-10 | 10 | 270 | 366.1 |
| 7/8"-9 | 9 | 395 | 535.6 |
| 1"-8 | 8 | 580 | 786.4 |
Grade/class comparison:
- Grade 5 (imperial) is roughly equivalent to Class 8.8 (metric): medium-strength steel bolts.
- Grade 8 (imperial) is roughly equivalent to Class 10.9 (metric): high-strength steel bolts. Torque values increase by approximately 40-50%.
- Stainless steel bolts typically use lower torque values (about 60-70% of carbon steel values) because they are more prone to galling.
Factors that affect torque requirements:
- Lubrication: Lubricated bolts require 20-30% LESS torque than dry bolts for the same clamping force. The tables above assume dry conditions.
- Thread locking compound: Medium-strength compounds (like blue Loctite) require approximately 10% more torque; high-strength (red Loctite) may require heat for removal.
- Material being fastened: Soft materials like aluminum or plastic need lower torque to avoid crushing or stripping.
Practical tips:
- Use a calibrated torque wrench for critical fasteners. Hand-feel is unreliable, especially for small bolts.
- Tighten bolts in a star or cross pattern when multiple bolts secure a single component (like cylinder heads or wheel lug nuts).
- Never use an impact driver for final torquing unless it has a calibrated torque-limiting mode.
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