Anderson window balance

A contractor from Patchogue NY says:
I have a double hung Anderson window and we need to change the string balances. It is and older unit with 3/8 inch thick insulated glass, wood frame inside vinyl clad outside, which part number would I chose.

Thank you
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Paul from SWISCO responded:
Thanks for contacting us, Frank. I can't say for sure. We would need to see pictures of each stamp printed on the balance box itself. I'm afraid that's the only reliable method of identifying the proper replacement balance.
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