21" Channel Balance 20-9
Hello, thank you for posting,
With this combination of attachments, you could have either an S378, S380 or S385 channel balance. You’ll need to measure as shown below. The Series 378 has a 7/8" deep bottom attachment while the Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment.
The 20 9 stamp does not directly translate to our spring stamp options. You will need to weigh the window sash and compare to the strength chart on the series product page to choose the correct option to support the window sash. Please review and let us know if you have any questions!
Since the sash weight is still under 27 pounds, you can use the 2050 stamp option that can support a 23-27 pound window sash.
Please see the S385-21 with a 2050 stamp option. Let us know if you have any additional questions!
