jesawdy wrote:I don't think the screw will prevent the burrs touching, when you change the burr set, the screw will be in a different orientation to where the burrs are touching.

That is correct. New burrsets, as you stated, would change the zero point and the screw's placement is not that accurate nor is it adjustable, so it cannot be an accurate stop point.

I suppose that the safety aspect of the burr unwinding itself is the real answer....

As they say, this is what happens when lawyers are needed to assist in the design of coffee grinders sold to the masses.

....but I always thought it was there so that people don't have "idiot" moments and turn the scale more than one revolution and get the thing 360 degrees (or more) out of whack.

It happened to me once. I had done a cleaning and was setting the zero point and the hopper slipped in my hand and it spun. Although the top burr was spun around a couple of times, there was no nuclear reaction nor did the top burr fly off and hit the ceiling. Unless the Rocky is really well worn or the threads have been lubricated, the burr/hopper assembly most likely will not be ejected from the grinder. You will get a really coarse grind and quick pulls until it is readjusted.