Creating a ring and preserving thickness while scaling in Illustrator
To create my rings, I use two instances of the Ellipse tool. Then, I center the two circles, and use the Pathfinder tool to delete the intersection. I am left with a thick ring. I make some copies of the ring. When I rescale, the thickness changes. How can I preserve the thickness?
Don't use the Pathfinder. There's no way to preserve the "thickness" of the ring when scaled. The thickness of your ring is an intrinsic part of the shape you made so it scales exactly the same as the rest of your shape.. The thickness literally is your shape.
Instead use a single path with a stroke. You can then adjust your stroke as needed and you can check "Scale Strokes and Effects" in the Scale dialog: