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· Eff U Gee Em
159 Posts
Discussion Starter · #1 ·
I just picked up a crowsfoot to use on a torque wrench (for my car). I remember reading a few years back that there is a multiplier you need to use to adjust the torque setting in order to get an accurate reading due to the extra length/leverage. Is this true? How do I determine what the multiplier is?

Realistically we're talking about a 3/4" difference here, I could probably just set the wrench for the required torque value without worry of over-tightening, it's a big nut, and steel-on-steel, but curiosity gets the better of me.


485 Posts
HamfisT said:
Turning the crow foot 90* will get it close enough.... unless you're working on spacecraft!
THIS is true, but just for fun...........
the formula is fairly simple.

For the example, I converted 20 Nm to 15 lbs/ft.

Imagine the crowfoot were 1 foot long. If it were:
( 1 foot x torque wrench setting) + torque wrench setting = final torque value

So if your wrench is set to 15 lbs/ft, a one foot long crowfoot would be:
( 1 ft x 15 ) + 15 = 30 lbs/ft . . . Or, double.

Find the 'distance between centers' on the crowfoot wrench you are using.

Express that distance as a decimal of 1 foot. If the 'distance between centers' were 2 inches say, then:
2 / 12 = .167 ft

Plug that number into the formula:
( .167 ft x 15 ) + 15 = 17.5 lbs/ft
Or simply: 1.167 x 15 = 17.5 lbs/ft

But in this example, 15 lbs/ft is needed.

And to figure that, take:
needed torque value / 1.167 = torque wrench setting

15 / 1.167 = 12.85 lbs/ft . . . Call it 13 lbs/ft
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