I decided to put some hypothetical numbers into their formula and yours to see if the results were similar and set up a test. If I want 100 ft/lbs of torque on a fastener and am using a 6ö extension, your formula indicates the following setting on the wrench scale would be needed:

I = A / 1+E

I = 100 / 1+.5
I = 100 / 1.5
I = 66.67 ft/lbs.

The same numbers into their formula and using my torque wrench handle length of 13ö:

TT = TA x IT / L

TT = 100 x 13 / 19
TT = 1300 / 19
TT = 68.42

Now, both answers can be wrong, but both answers canÆt be correct û although in that example they appear close. But if I used a torque wrench with a different length handle (say 24ö) and the same 6ö extension, it looks like this:

TT = 100 x 24 / 30
TT = 2400 / 30
TT = 80 ft/lbs.

So, how can that be? It does seem counter-intuitive that a longer length torque wrench would require a higher indicated setting to apply the same force to a fastener through identical extensions.

The reason for the need to include the torque wrench handle length in the calculation appears to be because of the relationship between the handle length in proportion to the length of the extension adapter as well as the internal design that includes 2 levers operating on a fulcrum or pivot. As the handle gets longer, the multiplying effect of the extension is reduced, since as a percentage of overall length, it has become less. Looking at it from the other way æround, if the extension was gradually reduced to the point of nearly zero length, the mechanical advantage provided by the extension is negligible and the wrench setting is dialed in to the original torque desired at the fastener.

All of the foregoing applies to ôclick-styleö torque wrenches û further, not only is the calibration of this type wrench affected by a forward extension, a handle extension will also affect indicated values. A handle extension will not affect values on a beam-type wrench.

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