I designed this simple D6 (6-sided) dice holder to hold a standard set of 12x (16 in mm size) Chessex dice like those found here. Should work with most similar types of dice, as 16 mm is more or less the standard size for these types of dice. It is customizable to different numbers of dice and size (see how-to-customize section below).

As a bonus, in the standard size provided, it fits almost perfectly in the excellent 3D printed mushroom box by 3DPrinty here (as pictured, listed as a remix, even though technically my dice holder design is original). The mushroom is not my work, and you'll need to download it from the link if you want it. My dice storage container here works alone by itself of course, but it was irresistible to put it in the mushroom design I had just printed :).

This holder is designed to hold 12 dice, 3 dice high in one of the 4 slots of this circular holder. The screw-on top keeps the dice secure during storage or travel in a small amount of space.

How to print/use:

• PLA or PETG should work fine as-is. I recommend PETG if you can, as it will likely wear better on the screw threads and is lower friction. Model shown is printed in PETG.
• Recommend printing at 0.16 layer height (for the threads part, at least, if you wish to use variable layer height).
• The cap and thread have been tested at different thread sizes and tolerances, and I'm posting one that works well on a variety of printers. If it's a little sticky at first, work it back and forth and it will quickly will become butter smooth. If you really want you can add a touch of PTFE lubricant (I love just a tiny bit of SuperLube brand grease), but this isn't needed.
• As pictured, this default size fits perfectly into the 3D printed mushroom box linked above, which is an unreasonable amount of fun for no reason I can tell.

The present design is simple and customizable for cube shaped dice of any number/size based on the included Fusion 360 file.

How to customize:

• For different Size dice: Adjust the DiceWidth parameter. Remember to leave a little tolerance for the size of the dice and room for them to slot in. For the Chessex dice I have, I measured ~16.3 mm width and set this parameter to 16.5 mm.
• For more/less than 12 dice (in multiples of 4) adjust the DicePerSlot parameter in the included Fusion 360 file. My default design adds an additional 2 mm vertical clearance to the total, but this is easy to change. This works in tandem with DiceSize. Yes, i realize this acronyms to DPS (damage-per-second) :).
• For other customization, such as the "holding" portion of the circular enclosure that retains the dice, you'll need to manually edit the sketches to make an overlap that suits your dice size.

Note: I haven't played extensively with customizing, but i've done my amateur best to make it easy for people. If improvements are needed, please tell me.