Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4302042.

A simple holder that holds your pi. Needs 4 m2.5 or m2 screws to hold the pi to it. Should work with Pi 3 or 3+ because it has the same mounting holes. I've only tested it with the pi 4b because I only have that pi. See print settings if you want the triangle pattern on the bottom. I put some rubber feet on mine to make it less slippery. If this does not work with pi 3 or 3+ please tell me so I can improve the design.