channel balance replacement

A home owner from Tracy, CA says:
Hello I just had a question regarding what part I need, I am unsure of what option to to pick based off of what we removed. I attached 3 photos of the part we removed. On the part it says 30 4 B.S.I 0L. The metal part we removed is 31'. Just wondering if you can help me understand the option numbers and what option number I should pick?

Thank you.
Thumbnail of the uploaded file named channel balance.jpg
Thumbnail of the uploaded file named IMG_20200331_154645290.jpg
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Casey from SWISCO responded:

Thank you for your question. Have a look at both our S380-31 and S385-31 channel balances. The balances appear to be identical in appearance, with the exception of the 'depth' measurement of the bottom balance shoe. You will need to measure the depth of your bottom shoe, the way it is shown in the diagram below, to determine which of the two balances would make the better replacement. Whichever one chosen will use a 3040 option that supports a sash weight of 23-28 pounds. 

Alternate view of 15-004
Alternate view of 15-004
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