Determining length for my Series 385 Channel Balance

A purchasing agent from Saint Lucia W.I says:
Hi,
I am looking for block and tackle channel balance as seen in the S 385 to fit a 48x36 and 36x36 single hung windows.

What inch will correspond to these windows ?

Thanks for your reply.
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Tom from SWISCO responded:
Hello! Would you be able to tell me the height of the visible glass for the sash this balance will be supporting? That will allow us to determine the proper length. Thank you!
A purchasing agent from Saint Lucia WI says:
Thanks for your quick response.
The hight of the glass is 10 7/8.
Thanks for your reply.
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Paul from SWISCO responded:
Hmm... I'm a little confused. The height of the visible glass does not correspond to the two measurements you gave before. To play it safe, would you be able to remove the balance from the window and send us a photo of it? The lengths will be the same but the stamped spring number will be different.
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