Business card case with invisible clamp - various sizes

I was looking for a simple yet functional business card case for... my business cards.
Most of the existing ones unfortunately don't have any information about the size the cards may have.
So I designed my own case and additionally gave it some "magic".
Inside of the case is a clamp that holds the cards in place. (In my case it even works with only one card left).

The current model offers place for about 15 cards, depending on the paper quality.

Not to make the same mistake I have inclu