Mail Flag insert
thingiverse
another mail flag insert insert fits into mail flag https://www.thingiverse.com/thing:4808204/edit
Download Model from thingiverse
With this file you will be able to print Mail Flag insert with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Mail Flag insert.