Sash balance replacement

Hello there. This looks like either an S351-15 or S390-15 Channel Balance. The only difference between these two balances is the 'depth' of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the diagram below for reference. Compare both balances with your old hardware to see what matches best. For a stamp option choose 1430.

Comparison of the S351 and S390 balance shoes.