Quote Originally Posted by nova_robotics View Post
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.
I've long wondered how those work. I understand the torsion rod principle (anyone who has fought a stubborn bolt would), but not how that ultimately limits rotation. Obviously the smaller diameter takes less torque to twist up, but that's where my understanding ends. It seems to me that the rod would store the energy until it reaches its limit, then stop twisting and transfer it on to the socket.

Neil