Vertical pen stand with inward curve

I think you can just plug it in, but it's safer to use adhesive.

The hole diameter of the M3 insert nut is 4.5mm.
I made a version with a screw hole only on the bottom, and a version with a screw hole on the top as well.
Both use the same bottom parts.

The pillar part is a pipe shape with a through hole.

Use M3 x Length 8mm or more

4.5mm diameter insert nut.