help identifying Milgard window balance

Hello,

With this combination of attachments, you could have either an S380-27 or S385-27 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. You'll also need 2640 spring strength options for your replacement balances.

Thank you and let us know if you have any other questions or concerns.

Comparison of the S380 and S385 balance shoes.

The 2640 strength option is based on the 26 4 stamp on your original balance but if you're sure that the sash weighs exactly 18 pounds, then you should go with the 2630 option since it's possible that someone installed balances with an incorrect spring strength at some point.