This is a spell counter for DD5 spell slots. It can work with regular D6 (16mm) or you can print the separate files for dice I made: faces are 4, 3, 2, 1, 0 (for no spell left) and blank (for "level still locked").
If you intend to paint the dice, you'll have to print them slightly smaller. 98% of the size should do. If you print them without a brim, expect the bottom side to be a bit larger. You'll have to slightly file this side for the die to fit in the counter.