Replacement balance springs

A quick learner from Orange County, CA says:
Window Mfg. is ATN number on old springs is 31 9 FX CMC 7 as pictured.
they are 9/16 wide, window is 34.5 high and 27 lbs
need 2 pair, 4 total springs
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Casey from SWISCO responded:


It looks like you have either our S351-32, with a 15-002 bottom attachment, or S390-32, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. You'll also need to know the weight of your window sash in order to choose the correct spring strength option since the stamp on your current balances is outdated. Once you choose the correct balances based on the diagram below, you can follow the chart under the product description to choose the correct option. 

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