Determining the sash weight #

A quick learner from Annapolis, MD says:
October 8, 2016
I've determined all info for ordering but am unsure about the ash weight code. There are numbers and letters stamped on the back o fate channel part. They are ; 27S30 stamped lengthwise and letters B S.I. Crosswise. The channel measures 28". I'm assuming it's a "B" weight?
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Paul from SWISCO responded:
October 11, 2016
Hello! I'm not sure. I think you might have a 30 pound sash, which would indicate our 28E option. I would recommend weighing your sash on a scale to confirm.
28" Series 770 Balance
28" Series 770 Balance
S770-28
$12.70
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