All you want to know is what torque to apply. Torque = force X distance (or lever arm), or, using some algebra, Force = Torque/distance. From your definition, the axis of rotation is the centerline of the bolt or nut. This is the same as the centerline of the socket/extension/square driver. So, the distance (in our formula above) is the distance from the centerline of the square driver to where you apply the load on the handle of the wrench.

What you are confusing this with is the resultant force that gets applied to the nut. In engineering, we do a lot of summation of moments. A moment is an engineering term for torque. Summation of moments means that if nothing is moving (or is static) then there has to be a reaction moment (or torque) equal to what you apply. This is the force that the nut resists with on the socket acting through some lever arm.




Remember from the first post that a 3 lb force applied using a 2 foot bar gives 6 ft-lbs torque, but a 12 lb force using a 1/2 foot bar also gives 6 ft-lbs torque. Clear as mud?