I had a window screen where the corner pieces holding the frame together came apart. Couldn't find replacements anywhere, so I made one as a project to learn OpenSCAD on. Figured sharing this might be useful for someone. I have no idea where these screens came from or what brand they are - they came with the house and aren't marked - so I figure they're more or less generic.

This is flat on the back so it doesn't need supports, but the tradeoff is that it doesn't perfectly match the originals. The part where it's different and you can see it doesn't  line up is in the back of the frame though, so it's worth it for me.

I printed these in Sovol white PLA. It's a pretty simple model and shouldn't need any special considerations- there is a tiny bit of bridging/overhang for the channel cutout, but everything else is pretty much a flat brick.

Parameter descriptions:

base_side=17.9; // Side length of the raise middle bit.
base_thickness=6.5; // Thickness of the raised middle bit.
wing_width=10.4; // Width of the wings. May need tweaking to fit well.
wing_length=35; // Length of the wings. 35mm barely fits in my windows.
wing_thickness=3.4; // Thickness of the wing parts. May need tweaking to fit well.
wing_offset=1; // How far from the "back" the wings are set off. Makes the part align better with the frame visually.
channel_width=3.3; // With of the channel for the screen gasket.