I had a swinging cat door in my basement door that the cat refused to use, so I created this frame instead. It comes in 8 pieces so each one would fit on my 235mm square Ender 3v2 bed.

The hole in the door needs to be about 82x165mm for this frame to fit inside; there's a 35mm trim piece around the whole thing so there is a little bit of wiggle room if it's a bit bigger.

There are four pieces for each the front and back that you assemble like puzzle pieces, and then each set is attached with a 50mm M4 bolt and nut. The holes are specifically designed for these hex socket head cap bolts, which I got in this set from Amazon: https://amzn.to/3NIuxBB

You'll notice from the pictures that those bolts don't actually go through the door, so your door hole just needs to be rectangular. Not that you are probably super worried about more holes in your door at this point, but it does make life a little simpler :)

Anyway I hope you enjoy!