strength of spring in vinal window channel balance

A home owner from ilion,ny says:
26" / 9/16" the only stamp on original channel is ( 2601 / BS1 Lk )

I'm guessing it is a ( 26B 1-1/4" shoe. )
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Tom from SWISCO responded:

Thanks for posting. I'm afraid I don't know what that stamp means. I see you were looking at our S775-26. Is this the Series and size you need? If so, I recommend weighing your sash on a scale and referring to the chart we show on that store page. That will tell you what option you need beyond any doubt.

I do not advise guessing or estimating the sash weight. It's important to be as precise as possible.

How to install a S775 balance
How to install a S775 balance
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