I lost track of the corners that my window screen kit came with and I decided to make and print my own.
This fits a Prime-Line (Make-2-Fit) 5/16" x 3/4" aluminum window screen frame. The kit is available on Amazon and many hardware shops like Ace Hardware.
I printed in PLA, 0.3mm layer height and got a pretty nice fit.
There are other similar designs online but they didn't fit my window so I made a new one.
The author marked this model as their own original creation.