Casey from SWISCO responded:
September 19, 2019
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. You'll also need to know the length of your balance and the weight of your sash in order to choose the correct option. Choose the spring strength options 2830 and 2840 based on the stamp on each balance. Comparison of the S351 and S390 balance shoes.
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