Window channels

Hello,

I can't be sure since the bottom fitting shown in your photos is damaged but your assembly reminds me of the S380-29 at first glance. I'd recommend removing an intact balance to confirm that the 1" deep bottom shoe matches yours. 

If so, your 28C stamp indicates that you would need 2830 strength options for your balances, which will support a sash between 16-23 lbs. Thank you! 

Close up view of the S380 balance top.

Close up view of the S380 balance shoe.

Your balance does resemble the S380 but you would need to remove the balance fully to confirm that the bottom fitting measures exactly 1" deep, which, unfortunately, we can't confirm from photos.