Not sure what these are called. They are made of plastic. They are about 1 1/2" long each way, and less than 1/4" thick. they hold the glass frame corners together and have a little nub that extends into the window frame and act as guides to slide the window and keep it in the track.
Emily from SWISCO responded:
June 21, 2022
Hello!
This reminds me of our 95-205 corner key. Look over our dimensions and compare them to yours to see if this matches up.