I wished they explained why turning the screw wouldn't work

Message:

That's a cool variation and a nice story and all, but in the cast of moving sand, why couldn't they turn the screw like everyone else did?

Conrad makes a good point about keeping stuff out of the bearings. Is that the only reason? Maybe it's sufficient. The old guy never explains anything more that "everything else was unsuitable".

I'm sure there was a reason, but by not explaining that part it makes it seem like no one ever invented this variation because it didn't need to be invented.

Yours,