Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3558094.
This simple cap is designed to fit a self-inking "Paid" rubber stamp, but it should fit any small stamp measuring 22.5mm x 52.5mm. The fit is really snug, but that was what I wanted. If you want a looser fit, I'd recommend printing at either 101% or 102%.
I know that this is a simple model, but it is my first attempt at moving from my 10 year de facto default SketchUp to FreeCAD, so be nice.
NOTE Due to either a Thingiverse bug or (more likely) shadowbanning, my models no longer show up under the [Newest] listings. If you want to see more of my models, please be sure to 'follow' me. If you print this, it would really help if you'd post a 'make' so that others could find this model.