Sash balancers

Thanks for posting. It seems to me you have either the S351-35 or S390-35. The only difference between these two channel balances is the 'depth' of the bottom nylon shoe, or the 'heel-to-toe' measurement. See below. Measure your old balance's shoe depth to see what matches best. For a stamp option choose 3420.

Comparison of the S351 and S390 balance shoes.