Here's an example of the type of shim I'm referring to:
They are sold marketed for various uses - tile spacers, leveling window or door frames, etc. They are non-tapered.
Its not clear to me why the specific horseshoe shape is beneficial. Why not just a simpler flat piece of plastic? Or a more conventional circular "washer" shape if a central open area is needed?
If anything due to the thinness of the material, the ones I've used (1/8" and 1/16") are pretty fragile, which is a slight disadvantage of the shape. (ie it covers a large surface area without commensurate strength).
I assume these were invented for some specific applications ... what are they?