Window balance identification

Thanks for posting. This looks like either our S351-25 or S390-25 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 with your old hardware to see what matches best. For a stamp option choose 2450.

Comparison of the S351 and S390 balance shoes.