Catan tile holder

I designed these tile holders for the 3rd edition Catan tiles for my wife's class when she teaches probability. She did not want 3d tiles, but needed something to keep it from getting knocked around and did not want to have to glue the tile down to the holder. All the other designs we saw did not hold the tiles together as much as we needed (kids can get a little rough) and it seemed that any walls I used on the outside to hide the magnets (5mm round) caused them not to hold as well as needed.