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Casey from SWISCO responded:
March 15, 2023
With this combination of attachments, you could have either the S380 or S385 channel balance. You’ll need to measure as shown below. The Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment. Based on the stamp codes you provided, you would need 1930 spring strength options for your replacement balances. Please note that a 1930 stamp would indicate that you should have a 20" long balance channel. As for your 21" balances, see the 2040 strength option on the balance product page. All of our balances have a chart under the product description so that you can confirm that the strength options that you choose will support your window sash weight. Thank you and let us know if you have any other questions or concerns. 
Comparison of the S380 and S385 balance shoes.
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