17" long

Thanks for posting. This looks like either an S351-17 or S390-17 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 with your old hardware to see what matches best. For a stamp option go with 1640.

Comparison of the S351 and S390 balance shoes.