Stackable puzzle sorting tray. Tried a couple of existing models but I did not really find them to my liking so I made my own. These are 20 x 20 x 2 cm. In order to avoid problems with warping and bed adhesion I opted for a pattern in the bottom, there are a few different patterns. I have not printed the one with the flat bottom myself but all the others I have printed just fine. There is a slight radius around the bottom to make it easier to pick up puzzle pieces.