Hangs from a wall mounted hook. Interior is 100mm long, 45 mm tall and 70 mm deep. Designed to fit a fat wallet. Also holds my 5.5" smart phone. The base of the holder has 2 hooks (5mm square cross section) to hold keys that were originally on that hook. The ring has a 30mm ID and a 6mm square cross section.

I wish I had had this when I was in college, where shelf space was minimal, command hooks were super useful, and being cheap was in style.