Pi hat spacer
thingiverse
These were mainly created for the Pi1541 hat found at https://www.hackup.net/2018/07/pi1541io-revision-4/. Nonetheless, I think it should work with most pi hats. I employed 2mm x 16mm bolts on my setup.
Download Model from thingiverse
With this file you will be able to print Pi hat spacer 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 Pi hat spacer.