Unknown Sash Balances

A contractor from Philly. 19130 says:

I removed this balance from an unmarked window. They are 26" long. 5/8 size. Spiral at one end and Block -and-Tackle at other. Note- the strings on B&T end feed opposite top and bottom...say, 9 to 3 at center and 12 to 6 at end.

No I'd markings. No tube covering. Exposed inside jamb behind slat type cover. Any info GREATLY appreciated.

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Bob from SWISCO responded:

Thanks for posting. This old arrow balance isn't made anymore. But it can be replaced by our Series 770. If your balance is 26" long, see our S770-26. To know what stamp option to pick, you will need to weigh your window sash, then match that exact weight with one of the weight ranges listed for each stamp option on the product page.

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