Side load channel guide

Thanks for posting. That stamp actually isn't an identifier--it tells us the strength of the balance. Channel balance identity is determined by the combination of nylon attachments at both ends. In your case, this looks like either an S351-17 or S390-17 Channel Balance. The only difference between these two balances is the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe'. See the diagram below for reference. Compare both balances with your old hardware to see what matches best. For a stamp option, you would choose 1640, just as your old balance is stamped. Also see the video below that goes into more detail about how to identify replacement channel balances. Let me know if you have further questions.

Comparison of the S351 and S390 balance shoes.