Plastic piece that holds grid inside window

Thanks for writing in. I am afraid we don't carry an exact match for this grid clip. I believe it's from an Atrium window. I am not certain this will work, but take a look at the 55-176 Andersen grid clip. This works on the same principle as your old one: it inserts behind the glass to put pressure on the grid and keep it in place. Take a look and let me know if you think this might work as a substitute.