A quick learner from Eagleville, PA says:
September 22, 2015
Owens Corning Fiberglass double hung window model: FDH has broken channel slider where the balance spring attaches.
Paul from SWISCO responded:
September 23, 2015
Check out your thickness and width, those are the two most important dimensions. See if they match our 15-047. I think this may be the match you need.