A handy person from florida says:
what is option d,option b,option c in regards to ordering for 15" series 770 tilt channel balance
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Donna from SWISCO responded:
You should check the balance you are replacing for any markings numbers and/or letters. The stamp options refer to different strengths.
15" Series 770 with stamp option
15B will carry a window sash weight range of 7 through 10 pounds
15C will carry 10 through 16 pounds
15D will carry 16 through 19 pounds

This information is based on 2 balances per sash. Balances are designed assuming friction in the jamb weather-strip will carry a portion of the sash weight. Suggested sash weights are approximate.
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