This is an 18 year old house with original double hung windows. Both the top and bottom windows are supported with a long spring that attaches to a hook on this sliding part, that fits into a channel. Image 2781, I've circled where the hook has broken off. I can supply measurements if needed
Dave Sr. from SWISCO responded:
May 28, 2020
This looks a lot like our 20-022 friction shoe. Look it over to see if this part is the one you are looking for.