please help identify channel balance

A home owner from Florida says:
its 29"

only markings I see is: 28C USB

I feel its a S380-29

how do I know what weight?

2830?

I need a bunch of these...
User submitted photos of a window balance.
Profile picture of Tom
Tom from SWISCO responded:
A stamp of 28C usually corresponds to our 2830 option, but you can always weigh your sash on a scale to confirm.
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