That is very surprising and totally fascinating. I have no intuition for why that works.
It is all about how far your hand is from the fastener, measured in a straight line. The socket that is welded to the extension bar is exactly as far away from the fastener as the user’s hand would be if the wrench was directly on the fastener. The extension is the same length as the torque wrench. When the wrench is 90 degrees to the bar, he creates an equilateral triangle. That is one where all sides are the same length. So his hand is exactly as far away from the fastener as it would be with the wrench directly on the fastener.
if he put the wrench in line with the extension with his hand farthest away from the fastener, he would effectively double the length of the wrench, thus applying twice as much force as the wrench is set for.
As he showed, with the wrench in line with the tool and his hand over he fastener, he could apply almost no torque.
Put another way, To tighten a fastener to twenty pound feet, we could apply twenty pounds of force with a one-foot wrench. (Our hand should be one foot from the fastener.) If we had a two-foot wrench and applied twenty pounds of force, we would be applying forty pound feet to the fastener. Twenty pounds times two feet equals forty pound feet. To get the correct tightness in this case, we would need to apply only ten pounds of force. Ten pounds times two feet equals twenty pound feet.
P.S. I am referring to the last video above.
