Anderson Sash Balance, R13/927 12-87 and L9/1327 12-87

A quick learner says:
I am in the process of replacing the sash balance for my Anderson windows. The two sash balances on my current windows are R13/927 12-87 and L9/1327 12-87. Which replacement parts do I need?
A customer submitted photo of Andersen sash balances.
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Tom from SWISCO responded:
Thank you for posting. Are both of these balances in the same window, or are they both for different sashes? If they're in the same window, please look at our 24-939 Andersen sash balance. This can be used to replace balance boxes with the stamp 9#27. Let me know what you think!
A quick learner says:
Yes, both of the balances were in the same window. The R13 was on the right and the L9 was on the left. If this still seems correct, I will look at the 24-939 sash balances.
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