After lots of tests, I ended up with this design.
It's just another "Bottle Cap Opener".

but:
- Higher to accept different caps diameter.
- Big enough to help unscrew caps but not too much. (Let's save filament).
- Ergonomic Design to fit Thumb-Index grip.
- Large top hole to let expel caps.
- Little hole to tie it up to something and never loses it.
- "Direction of Usage" top sign to help those who just can’t get into it. (my wife)