My set of ER32 collets arrived in grease proof paper – or whatever the brown stuff is called, so a storage board was needed. I made mine from a piece of white 'plastic' food preparation board. Just drilled a series of holes slightly smaller than the max. diameter of the collet. The sides are tapered to give a slight angle for easy selection and they are screwed to the main board.
No chipping or oil soakage sith this material and it's easy to keep clean. Only possible downside is that I can't attach a size tag for the collets to the board – glue won't stick!
Dave
The Emerald Isle