Not sure what the technical term for the part is, but it is the metal piece that allows the lower window to fold open so that it can be removed. On the part there is a the following part number, I presume: 2369R. The picture shows the part broken. The end was flush but it twisted and broke off of the main body portion of the part.
Casey from SWISCO responded:
September 8, 2017
Thank you for writing to us. This is known as a pivot bar. It looks like our 26-164 is a good match. Please check out the measurements and compare them to yours. Let us know what you think.