It's a case for old cassette tapes, it's a variation on the case I made for Game & Watch machines, as I noticed it was about the size of a cassette and I had a few cassette lying around that need a case. Apart from the size I also added those little things in the middle of the spools to stop the tape unwinding in the case. I need to figure a way to hold a card with notes like old cassettes cases used to have. Until then this will have to do.