28 4 BV CMC 7 - - IS THE MARKING ON THE CHANNEL BALANCE

With this combination of attachments, you could have either an S380-29 or S385-29 channel balance. You need to measure as shown below. The Series 380 has a 1" bottom attachment, and the Series 385 has a 1-3/32" attachment. It also seems like your old balances were too strong for your window if you had balances with a (28 4) stamp in a window with a 16-pound sash. I would recommend going with a 2830 option that supports a sash between 16 to 23 lbs for your replacement balances. 

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

Comparison of the S378, S380 and S385 balance shoes.