My Depth Collar holder - designed specifically for FAMAG depth collars, but I imagine others would work (sizes 3, 4, 5, 6, 8, 10, 12 mm) -(you'll note I have two for the 4mm size because my kit was missing the 4mm and they sent me two 4mm as a replacement)

On my photo, it's missing the last two minutes of printing (user error…my filament jammed and after I fixed the jam I hit cancel rather than resume) - that's why the colouring of the 3 and 12 is not finished. I didn't want to waste filament re-printing it just for those last two minutes!