This is a very simple SD card holder, the size of a credit card, which fits in a wallet. It's designed to be slim so that it should be able to slip into any credit card slot. It holds two standard SD cards, one mini-SD card, and one micro-SD card. Mini-SD isn't very popular as far as I can tell, but I didn't think anyone would need TWO spare micro-SD cards so I went with the mini instead.The general idea is that you can carry spare cards for your phone, camera, or whatever. [Actually, if anyone is interested I could probably replace one of the cards with a spot for a SIM card.] I prefer keeping my keychain light, so I'd rather have this in my wallet than a USB stick on my keys when I need to transfer or store data.Complete with rounded corners and divots for easy removal. :)I actually made a version of this by cutting up business cards about a year ago, but the paper was too weak to really work. Hopefully this will be rigid enough to keep the cards in place and protected. There is no lid because I designed the cards to fit tightly, and once it's in your wallet there should be no danger of any falling out. But if they aren't secure enough I'll add some kind of cap.