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Crow’s foot spanners and torque wrenches

Adrian Saunders

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It depends on which direction the crows foot is pointing.  If it’s at 90 or 270 degrees  to the shaft then it makes virtually no difference to the breaking torque, but if it’s at zero degrees (Out the front of the wrench) it increases the breaking torque and at 180 degrees it decreases the torque.  In a test just now with my torque calibrator, a crows foot that has 20mm between centres increased the torque by 5% at 0 degrees and decreased it by 5% at 180 degrees.  
Of course, when one has a torque calibrator available It’s an academic question as one sets the breaking torque with the crows foot fitted 😀

The following formula has been used:

  • M1 = M2 x L1 / L2


  • M1 is the torque setting of the wrench
  • M2 is the actual torque applied to the nut
  • L1 is the normal length of the wrench
  • L2 is the extended length of the wrench



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most dont change the length of leverage by much to worry about if the drive is close to the foot 

but buy as example  100 ft lbs  is 100lb at a length of 1 ft  turn it into inch lbs by X 12 and divide the sum by the length say 14"  = 85 on the wrench 

or thereabouts 


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On 19/06/2020 at 07:53, KevinR said:




KevinR why is the length of the torque wrench taken from middle of the handgrip.

But I think I have just answered my own question with because it is where you push/pull on the torque wrench.


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