I have removed the old sash from my windows- see pics above. The only numbers on them are 11600-17 and BF 17 9#27 2/87
And my second window has 11600-17 and BFG (or 6) 10#31 12-86 stamped on it.
Tom from SWISCO responded:
May 16, 2018
Hello, thanks for your post. It looks like your balance with the "BF 17 9#27 2/87" stamp can be replaced with our 24-939 Andersen Sash Balance. The BFG (or 6) 10#31 12-86 stamped balance can use our 24-1033 as a replacement. Hope this helps!