[jyl]

I didn’t understand this at first, now I think I do.

Suppose you are looking at the head of a nut and want to turn it clockwise, with an adjustable wrench with handle to the right of the nut, positioned to engage the upper and lower flats of the nut. The pressure points are the right corner of the upper flat and the left corner of the lower flat. These two corners - upper right and lower left - are the only part of the nut that matters. The line between them is a diagonal, from the inner end of the upper jaw of the wrench to the outer end of the lower jaw. When you turn the wrench clockwise, you are effectively trying to turn that diagonal. As you do so, the upper right corner of the nut is pressing up on the inner end of the upper jaw of the wrench, and the lower left corner is pressing down on the outer end of the lower jaw. With me so far?

The choice you have is, are you a) applying pressure on the inner end of the fixed jaw and the outer end of the adjustable jaw, or b) on the inner end of the adjustable jaw and the outer end of the fixed jaw?

The fixed jaw is beefy, it doesn’t care what end is getting pressure. So the choice boils down to a) applying pressure on the outer end of the adjustable jaw, or b) on the inner end of the adjustable jaw?

a) is the wrench held rightside up (adjustable jaw on bottom), while b) is the wrench held upside down (adjustable jaw on top). [EDITED]

If you choose a), the force is being applied on the outer end of the adjustable jaw, and the adjustable jaw is trying to rotate relative to the wrench, and the slider is getting jammed and thus taking some of the force.

If you choose b), the force is being applied on the inner end of the adjustable jaw, and the adjustable jaw is not trying to rotate, but rather is trying to slide, so the teeth and worm gear are taking all the force. Since the teeth and worm gear are not perfectly aligned, only one tooth and one spot on the worm gear are taking all the force - it is whichever tooth/gear spot have the tightest fit.

Seems to me the slider is stronger than one tooth/spot on worm gear - the slider is 1” long and beefier than the 1/8” contact of tooth and gear. So you want a) [EDITED]