Stamp option for Owens-Corning Window

A home owner from chillicothe, mo says:
Please find attached 3 pictures of my broken Ownens-Corning channel balance. As you can see, it is 22" overall & I believe it is the Series 770. I have included a picture of the only stamp I could find on the channel. Could you help identify as to A,B etc?
User submitted photos of a window balance.
Profile picture of Paul
Paul from SWISCO responded:
I'm not sure, "21TG" does not correspond to any Series 770 option. Your best bet is to weigh the sash and refer to the chart shown on the S770-22 store page.
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