I also found it a useful analogy. Or rather, that was the way I thought of it. First I had to think about what would happen if the top bold, instead of rotatin

I also found it a useful analogy. Or rather, that was the way I thought of it. First I had to think about what would happen if the top bold, instead of rotating around a bolt, rotated around a band that wrapped straight around the other shaft. It stood to reason that the bolt would move backward away from the band, as the band moved along the spiral. (Whether it moved outward or inward ended up being irrelevant.) Then I went back to it being two bolts, and visualized the movement from the head of each. In one, the other bolt moved clockwise, and in the other, the bolt move counter-clockwise. So it stood to reason that one bolt would want to move away from the other, and the other move towards. So they would stay stationary.