need help identify parts windows balancer 2

Hello there. It looks like you have either the S390-17 or S351-17. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement. See the illustration below. Compare both with your old hardware to determine which you need. In either case, for a new stamp option choose 1620.

Comparison of the S351 and S390 balance shoes.