An index card holder which I designed for my friend, as he didn't find any good ones that fitted his needs.

It's made for A6 (105mm x 148mm) cards, but it should be possible to just scale it up or down (e.g. A7, A5, etc.) when you resize it with the factor ~1.414 (= squareroot of 2). The height (in the case of the starting position the y-axis) can be adjusted to your needs.

Example for A8 cards: resize x- and z-axis (and in this case also y-axis) to 100/(1,414^2) = 50%

Happy printing (and learning)!