Coil Balance

A home owner from O'Fallon, IL says:
Looking for 2 coil balance springs. The strap is about 3/4" wide. The only markings I found was "4075" near end of strap. Window manufacturers unknown, installer out of business.
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Tom from SWISCO responded:

Thanks for posting! This spring looks like a match for our Series 170. The stamp you have is a little weird, though. Can you confirm that that's last digit is a 5? Looks like it might be an S, but it's hard to tell.

If it is an S then I think we can safely ignore it. I would recommend the S170-407.

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