Fits square copic markers, about 12 of them. Feel free to re-jigger my .f3d file to suit your application. I printed this in "clear" PLA, on the side. I used supports, but it's up to you and what you decide is necessary.

I have had an issue with the axis of print being a little too tight, so maybe scale it all up by 1-2% and see if that makes things any better.

If this comment is still here, then I've probably forgotten to add photos of it.