Anderson Window Balance Identification

A quick learner from Manassas, VA says:
My double hung windows are 29 years old. Openning is approx 28"x61". Top sash is 31" tall, bottom is 31.5" tall.

Looking at the balances, the left one (looking on inside) has numbers F1 8 31 2 0 stamped on it, the right one has 11600-2 on it.

do you have replacements for these models ?
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Tom from SWISCO responded:
Check out our 24-837 . This can replace balance boxes with the stamp 8 31.
How to replace an Andersen Window Balance
How to replace an Andersen Window Balance
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