My collet collection was getting out of hand and I couldn't find a suitable (Gridfinity) based organiser that suited my needs.

Features of this are:

• Gridfinity based (2x4)
• It's not stackable... I wish it were, but I played with various ideas and it was just too difficult to get the things out with tall outer walls
• ER16
• tapered walls (so collet fits snugly)
• straight rows to allow organisation by size (row of 3mm, row of 4mm, etc)
• half "gridfinity height".

I printed mine using PETG as it seems coolant proof (although I would in general carefully clean collets before stacking). Fit is decently tight on a range of collets (amazingly not all collets are the same size...)