Balance identification

With this combination of attachments, you could have either the S378-29 or S380-29 channel balance. We can't confirm the exact size needed based on a photo but see the diagram below. The Series 380 has a 1" bottom attachment, and the Series 378 has a 7/8" attachment. 

Comparison of the S378, S380 and S385 balance shoes.

It also looks like the stamp code is spatially visible in your image below, which you'll need to choose the corresponding strength option. There is also a chart on the product page that explains how to choose your option based on the sash weight. If the balance stamp includes CMC or Caldwell, please let us know. Thank you and let us know if you have any other questions or concerns.