@TerraMex:
Where the double-helix passes through the float, the openings in the float are fairly oversized to prevent binding.
The rod is not an endless screw--that would cause a great deal of resistance. Rather, it is more like a hexagonal rod, or a round rod with a single flat side, or really any shape that is 'keyed' and has the same cross-section over its entire length. It is meant for the float to move freely in the vertical direction, but it needs to have a shape that allows it to be 'locked' to the float, in the sense of rotation.
Lastly, the float has to have some weight to it, but not much. Just enough for gravity to be able to pull it down over the double-helix, and overcome the resistance of rotational friction, and whatever the guage imposes. Usually the double-helix is quite steep, with maybe only 90-100 degrees of rotation over its entire length (~8" in my experience), so those forces are pretty minimal.
Also, in the application I've seen these used (gas tanks for snowmobiles) all parts are constantly washed in a gasoline/2-stroke motor oil mixture, so everything is quite well lubricated, and free to move.
Even though, I think it could effectively be scaled down, if someone still wanted to use a mechanical level indicator.
Actually...it could make for a very nice indicator to be installed in a tall cylindrical res...
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