I replaced a missing screen in my house and it kind of just fell back into the house. I guess the old screens had some spring mechanism built into them to hold them in place. There was a little groove that runs around the entire inside lip of the window frame, so I designed a little retainer clip to hold the screen in place, with a notch on the front side, so it would be easy to remove later if I needed to.
Yes, I need to clean my window... leave me alone.
Print settings don't matter too much... If you print a few of these, each one would only be holding back a tiny bit of weight in even the strongest winds... That said... they're little bits of plastic... don't count on this to hold anything. I'm not responsible if your pet or child pulls out the screen and jumps out of the window. Come to think of it, I'm not responsible if they pull them out and swallow them... I bear no responsibility here. At all. Don't eat these.