Overview:

I store my CNC bits in the plastic storage cases that they come in.  However, sometimes I buy bits that do not come with cases, or they come in larger-than-necessary cases.  

I made these to use in gridfinity containers that I also designed based on Zach Freedman's system: https://www.nexprint.com/en/models/G7191081

The plugs should be made from TPU, and there is a ribbed and non-ribbed version.  The standard one works well in the cases I designed, but the ribs help when using your own plug in a purchased storage case.

Note, the cases have slots in the side to allow circulation in case bits have any sawdust or moisture on them when you put them away.

Printing:

I recommend printing the plugs in TPU.  The case can be printed in any filament.  No supports required if printed in the orientation shown.