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Technical Reference
Torque Specifications
Torque-tension relationship chart for metric fasteners. Use this guide to ensure proper bolt tightening for clutch installations.
Bolt Class Explained
- Class 4.6 - Low/medium carbon steel, general purpose
- Class 8.8 - Medium carbon steel, quenched & tempered
- Class 10.9 - Alloy steel, high strength applications
- Class 12.9 - Alloy steel, highest strength grade
Surface Conditions
- Lubricated - Oil or anti-seize applied (K=0.15)
- Zinc Plated - Zinc coating, dry (K=0.17)
- Plain & Dry - Uncoated, no lubricant (K=0.20)
How to Use This Chart
1. Identify your bolt's property class (marked on bolt head)
2. Find the nominal diameter of your fastener
3. Select the appropriate surface condition
4. Use the corresponding torque value (ft-lbs)
Important Caution
All material included in this chart is advisory only. Extreme caution should be used when using a formula for torque/tension relationships.
Clamp loads are estimated at 75% of proof load for specified bolts. Torque values can only be achieved if the nut (or tapped hole) has a proof load greater than or equal to the bolt's minimum ultimate tensile strength.
Under/over tightening of fasteners can result in costly equipment failure or personal injury.