single hung Millard vinyl window balance

A home owner from Los Angeles says:
The balance string snapped. The balance is 1/2" x 21" and has the following marking: 20 4 CW CMC 10.
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Bob from SWISCO responded:

Thanks for writing in. See our S350-21 . Just go over all the dimensions the nylon fittings to confirm they match what you have. You'll need a stamp option of 2040. 

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