Salvo wrote:
No one nailed it.
You're missing the point. Extensions act as torsion springs! The amount of force the spring gets energized must be subtracted from the force applied to the bolt being torqued. The skinnier or longer the extension, the greater the error.
This error will probably be extremely small, but the OP has a valid point that should be considered in extreme cases.
For a hand torque wrench, this doesn't matter, as the torque is steady and the system is basically in equilibrium so far as the spring is concerned—this is statics, for all practical analytical purposes, not dynamics. The force is transmitted through the spring when the system is in equilibrium. (If you lie on an innerspring mattress, your full weight is transferred to the bed frame through the springs of the mattress. They don't absorb the force or anything once you stop bouncing around. It's the same thing here.)
For an impact wrench, this is a valid concern, since it's very much a dynamic system and not at equilibrium or sufficiently close to that to analyze it as such.
