you know what it is, this?
it's a salesman's' case. for brass instrument mouthpieces. there's one missing from the case because it's in my trumpet case.
i bought it from a guy i know a long time ago for about twenty dollars. i only needed one mouthpiece, but he had this cool case.
he also had a problem with accumulating too much musical stuff and his wife rather insisted he periodically sell things to make room.