Window Balance Unique 28-D-40

A home owner from Sorrento, FL says:
These are 29". Not sure what the markings indicate. Looking for 20 units for replacement.
User submitted photos of a window balance.
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Tom from SWISCO responded:
We believe you may need our S385-29 or S380-29 channel balance. Carefully compare the measurements of the balance shoes to determine which balance to choose. As for the option, you choose the 2840 either way. Get back to us and let us know how you made out.
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