Searching for channel balance

This appears to be either an S380-21 or S385-21 Channel Balance. 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. In either case choose 2050 for a new stamp option. 

Comparison of the S378, S380 and S385 balance shoes.