Jasmine from SWISCO responded:
May 10, 2023
Thanks for writing in! You are correct, your balances do appear to be either the S351-27 with a 1" shoe or the S390-27 with a 1-1/8" shoe. To determine which series is needed for your window. Look over the dimensions from the diagram below to confirm the depth of your bottom shoe. You'll need to select the 2640 stamp.
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