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[nova_robotics]

Now there is a little loss in the sockets between the extension and the socket end. But not that much. A few percent at the most. Actually thinking this through that may be erroneous as well. If the rotation is blocked where in the ratchet - extension - and then socket is the torque disappearing to? Potential twist in the extension shaft. That is about it as far as I can think through.

I actually worked this out one day and it's pretty interesting.

If you're using an impact then the "springiness" of the extension will limit the torque at the bolt. The extension is essentially a torsion rod and the impact is energy (or impulse?) limited. So some of that energy will go into doing work on the torsion rod instead of being transferred to the bolt. Somebody has already noticed this and turned it into a product. You can buy torque limiting extensions off the shelf.

BUT! If you look at what happens at the extension when you have a conventional torque wrench on there, the extension is sloppy at both end connections. It will bend over a few degrees in the direction of the force applied. That actually increases the effective lever arm distance between the point load (your hand) and the bolt. So if your torque wrench is set to exactly 100 lbs-ft, the fastener will experience a slightly greater torque, say 102 lbs-ft. The effect is small, only a few percent. But still. Opposite to what everyone assumes will happen.