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Bob from SWISCO responded:
June 21, 2021
Hello there. If I follow, you're requesting balances for two different windows. Do these balances have the exact same nylon fittings on each end (both with wings, or 'side tabs')? If so, and if the metal channel on each set of balances is 36" long, then you need either the S380-36 or S385-36. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. See the diagram below. You then have to choose a stamp option, which designates the balance's spring calibration. Now, you show a balance stamped 3540 in your photos. This stamp option supports a window sash in the weight range of 23 through 30 pounds. This doesn't match either of the sash weights you provided. Are you certain these are the exact sash weights? Did you ever have trouble opening or keeping these windows open, prior to the balances breaking? If so, let me know; also let me know if some balances have a different stamp code than others. 
Comparison of the S380 and S385 balance shoes.
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