Casey from SWISCO responded:
May 25, 2023
Hello, It looks like you have either our S351-29, with a 15-002 bottom attachment, or S390-29, with a 15-001 bottom attachment. Take a look at the image below to determine which balance you'll need. Based on your 17A stamp, you'll also need a 1710 spring strength option for your replacement balances o support a sash between 5-8 lbs. Thank you! Comparison of the S351 and S390 balance shoes.
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