Window channel balance

Thanks for posting. This appears to be either an S351-28 or S390-28. The only difference between these two balances is the depth of the bottom nylon shoe, or the 'heel-to-toe' measurement, so compare both with your old hardware to see what matches best. See the diagram below for reference. In either case for a new stamp option choose 2740.

Comparison of the S351 and S390 balance shoes.

If your shoe depth measures 1-1/16", then odds are it started out as 1-1/8" when it was brand new. These are only made of plastic so friction from constant use tends to wear them down over time. With that in mind, my recommendation would be the Series 390.