I think it's called a widow tilt pivot stop. And I think it was made between 1960to 1980. I also think it was made out of Teflon. I don't know who made the windows. We are missing some of these and trying to identify and locate them.
Paul from SWISCO responded:
December 16, 2019
The part you're showing looks similar to our 37-001 . Start with taking a look at the part and see if your measurements match up with ours.