A quick learner from columbia sc says:
January 3, 2015
The old one is 5737877 stamped on it and new ones are needed. Can you get this or a substitute? My windows are MW twinseal vinyl single hung 58" height x 34" width. The current one has a black shoe on the bottom with plastic hook at the top. The length of the balance is 32.5.
Paul from SWISCO responded:
January 6, 2015
I think you might have something like our Series 850 crossbow balance. Look it over and let me know if you agree. It is no longer made with that top hook (or in general, for that matter; we have a limited supply), however you can screw the balance in by using our 26-200 screw plug, which inserts into the jamb, and our 33-016 screw.