Looking for 2850 30 in balance

Thanks for writing in! Your channel balance reminds me of our Series 377 with a 19-018 Pan Am, Channel Balance Top. Although, since yours is stamped with a 2850, I believe you'll need the S377-29which has a 29" channel length. This is the measurement for only the metal channel and does not include the attachments.

The compatible top sash guide appears to be the 18-042 Pan Am, Top Sash Guide Pair. To confirm that these are the right replacement, carefully look over the dimensions below.

Detail of 18-042

Alternate view of 18-042