2730 window balances

Thanks for posting. That stamp refers to the strength of the balance, but not its identity. The identity is based off the attachments that you've helpfully provided photos of. This is either an S351-28 or S390-28. The only difference between these two channel balances is the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe'. See the picture below. Compare both with your old hardware to see what matches best. In either case, for a stamp option go with 2730.

Comparison of the S351 and S390 balance shoes.

Sounds good! Let us know if you have any other questions, and thanks again for reaching out to us.