It's a piece that holds the stationary window in place
A home owner from Rockford illinois says:
May 3, 2020
I would like to know what this part is and see if I can find a replacement for it.
Tom from SWISCO responded:
May 6, 2020
It's tough to make out what this part is, but it reminds me of our 80-051. This is a clip used to secure patio doors, though, not windows. Do you still think you could get it to work?