unknown brand spiral balance -no color coding or markings found

A handy person from Louisville, Kentucky says:
Hello, I would love some help in identifying some suitable replacements for quite a few spiral balances. These are for some large windows in a school building. These all have balances for both top and bottom sashes. The original balances have flimsy plastic sleeves that have broken on numerous windows or they are missing balances entirely. The windows vary in about 3 sizes throughout the building. I assume I will need to weigh the window sashes for each representative size, but I would love to see if you have an item that will replace this once the weight is known. Thank you so much.
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Tom from SWISCO responded:

These look like some old fashioned balances. Based on what I see here I feel confident that you an use our Series 500 spiral balance as a replacement, along with a bottom bracket like our 17-012 (sold separately). These have metal tubes so they won't become brittle like the originals.

We've used the Series 500 to repair old wood windows like this for years and years. It's a straight forward and effective solution that's never let me down.

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