A handy person from jacksonville florida says:
February 13, 2014
Tom from SWISCO responded:
February 17, 2014
Hey, thanks for posting. I've narrowed this down to two possible channel balance Series: either our Series 351 or our Series 390 balances.
Now, as you can see, there is only one difference between these two Series, and that is their bottom shoe. The Series 351 uses the 15-002 while the Series 390 uses the 15-001. I can't quite tell what you have based on your pictures, though. Please carefully compare their dimensions to your own hardware and see which is a better match.
I recommend you use an undamaged balance to determined this. Ideally, you would use the other balance in the same window, but if you have an identical window elsewhere in the house then that could work, as well.