Channel Balance ID

Hey Joe. This looks like either an S380-17 or S385-17. The only difference between these two balances is the depth of the bottom nylon shoe. This can be thought of the 'heel-to-toe' measurement. Compare both with your old hardware to see what matches best. You will need a stamp option of 1640. Let me know if you have further questions. And thanks, be safe as well! 

Hey Joe. If the metal channel, not including the nylon fittings, is indeed 16" long, that would be pretty unusual for a balance stamped 1640, though not unheard of. A balance stamped 1640 is typically 17" long. Those first two digits in the stamp code are supposed to represent the visible height of the glass in the window sash. The metal channel is 1" longer than the visible glass height.

If your balances are indeed 16" long, most likely what happened is that they were cut down by whoever built the windows to make them work. Often builders are limited with the parts they have, and in a time crunch they may simply modify the balances they have to make them work. So, if the shoe is 1" deep, and if the length is 16", then yes, you need the S380-16. The stamp option of 1550 does have a weight range that partly overlaps with the 1640 option; but I would get the exact weight of your window sash just to be extra safe. You can then confirm if that exact weight falls in the 1550's weight range of 13 through 17 lbs.