KEVOS® MAKEOS · Fasteners
Torque Wrench Adapter Check (Extension Correction, Actual Torque, Bolt Preload)
When a crowfoot or extension adapter lengthens my torque wrench, what should I set the wrench to, and what torque and bolt preload does a given setting really give?
Correction of a torque wrench used with an extension adapter: the effective lever length from the wrench length and the adapter length at its angle, the actual torque at the bolt for the wrench setting, the setting that gives the target torque, and the bolt preload and share of proof load from the actual torque with the nut factor (as the bolt torque and preload tool), against the target preload and the largest share of proof load allowed.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Wrench length (hand grip centre to square drive) | mm | Length from the centre of the hand grip to the square drive of the wrench. |
| Adapter length (square drive to bolt centre) | mm | Length of the adapter or crowfoot from the square drive to the bolt centre. |
| Adapter angle to the wrench (0 = straight in line) | ° | Angle between the adapter and the wrench (0 in line, 90 at right angles, 180 folded back). |
| Wrench setting | N·m | Torque the wrench is set to. |
| Bolt | ||
| Nominal diameter | mm | Bolt nominal diameter. |
| Thread pitch | mm | Thread pitch. |
| Nut factor K | Nut factor (about 0.2 dry, 0.15 lubricated). | |
| Proof strength of the bolt | MPa | Proof strength of the bolt. |
| Target preload (% of proof) | % | Preload wanted as a share of proof load. |
| Preload tolerance (±) | % of proof | How far the preload may be from the target. |
| Largest preload (% of proof) | % | Highest preload accepted. |
Method and formulas
- Effective length = L_w + E cos φ; actual torque = setting × effective length ÷ L_w.
- Setting for the target torque = target × L_w ÷ effective length, with the target torque from the nut factor (as the bolt torque and preload tool).
- Preload = actual torque ÷ (K d); share of proof = preload ÷ (S_p A_s) (as the same tool).
- Example: the setting gives 91.125 N·m at the bolt; set 80.896 N·m for the target; preload 75.097% of proof.
Limitations
- Wrench held at the grip centre; holding it elsewhere changes the effective length.
- Nut factor scatter dominates the preload accuracy, adapter or not.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Set a torque wrench used with a crowfoot spanner
- Check a bolt tightened through an adapter
- Avoid overtightening with extensions
Who it is for
- Fitters
- Maintenance technicians
- Quality inspectors
What you get
- Effective length and correction
- Actual torque and the setting for the target
- Preload and share of proof
Interpreting the result
- An in-line adapter makes the wrench read low: the bolt gets more torque than the setting unless it is corrected.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1535. Topic reference; no source tables or recommended settings are reproduced.
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Open the Torque Wrench Adapter Check (Extension Correction, Actual Torque, Bolt Preload) calculator
