@RonHarding Ah, now I see. And it actually seems like a useful tool for something I've had issues with as well. I usually try to scrape the stone using some piece of scrap stainless steel, but it never turns out as flat as I want it.
@CeesMeijer_7801 It's a tool to shape the surface of a grinding stone to make sure it's flat and spinning true. You can't sharpen knives on a wobbly stone.
@RonHarding Nice! Though I cannot really see what the project is...
Used these knobs in a project of my own: https://www.printables.com/model/501167-wet-sharpener-stone-truing-jig