Help identifying channel balance.

A quick learner from Roslyn, NY says:
I have to replace the channel balances on a few of my Fiberlux non tilt vinyl windows. I measured the balance to be 20" as you showed in the video. The search showed the replacement to be a 20" Series 350 balance. My balance has a 19 D stamp on it and I'm not sure how to figure the sash weight in order to purchase the correct replacement. Please advise. Thanks
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Paul from SWISCO responded:
A stamp of "19 D" usually corresponds to our 1940 option, but you can always weigh your sash to confirm.
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