Spiral balance replacement

A home owner from USA says:

I need to replace old spiral balances in single hung, non-tilting windows. They are unmarked; no stamped letters, etc. of any kind.

They are 35" long, and 9/16" in diameter. Not sure of exact weight of sashes, but they can't weigh more than 15 or 20 pounds.

What do you recommend ?
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Paul from SWISCO responded:
I recommend looking at our S500-35 spiral balance with a Red Tip (which supports sashes weighing 12 through 30 pounds). This is what we typically use for old wood windows that use spiral balances. Are you also going to need a bottom bracket? If so, see our 17-012.
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