Torque Wrench Extension / Crowfoot Correction
The wrench setting a crowfoot or in-line extension demands, which bolt-torque never gives.
Example
You enter
- Target torque at fastener (ft-lb) 100
- Wrench lever length (in, drive to grip) 18
- Crowfoot / extension length (in) 3
You get
- Wrench setting (ft-lb) 85.714
- If set to target instead (uncorrected) 116.7 ft-lb at the fastener
- Effective added lever 3.00 in
Details, formula, and sources
TW = TA x L / (L + E cos(angle)), the target torque scaled by the wrench lever L over the lengthened lever. A 3 in in-line crowfoot on an 18 in wrench targeting 100 ft-lb means dialing 85.7 - set it to 100 instead and you apply 116.7 ft-lb, a 17% over-torque that snaps small fasteners. Swing the crowfoot to 90 degrees and cos goes to zero, so no correction is needed - the field workaround. A shop aid; the calibrated wrench and the manufacturer's torque spec govern.
E_eff = adapter_length x cos(adapter_angle); TW = target x wrench_length / (wrench_length + E_eff); actual_if_uncorrected = target x (wrench_length + E_eff) / wrench_length; correction_pct = (TW - target) / target x 100.
Standard torque-adapter correction (Snap-on / FAA AC 43.13.1B torque-wrench extension relation) by name; first-principles lever statics.
The torque-adapter relation TW = TA x L / (L + E) is a public result; FAA AC 43.13.1B is free at faa.gov.
Estimate. AHJ and licensed professional govern.
Field names used by the API: target_torque_ftlb, wrench_length_in, adapter_length_in, wrench_setting_ftlb, uncorrected_actual_ftlb, effective_extension_in
- Effective lever TW = TA x L / (L + E cos(angle)); an in-line adapter lengthens the lever and lowers the settinglever statics
- 90-degree adapter a crowfoot square to the handle adds no effective length (cos 90 = 0) and needs no correctiontorque-adapter practice
- Calibration governs the calibrated wrench and the manufacturer's fastener torque spec governscope of this tile