What window balance should I order?

A home owner says:
My window balance looks like S380-27. Its stamp says"86 26-3 GM5 CMC 87". What balance should I order?

Thank you,

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Tom from SWISCO responded:
I'm afraid I can't be sure what you have. The stamp only tells us how strong the spring is. Your best bet is to carefully go over the pictures, dimensions, and information we show for the S380-27 and its two attachments, the 19-005 and 15-005, to confirm that everything matches up.
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