1/2 by 19 window balnces

Thanks for posting. This appears to be either an S385-18 or S380-18 Channel Balance. The only difference between these two balances is the depth of the bottom nylon shoe, or the measurement from 'heel' to 'toe'. See the illustration below for reference. Compare both with your old hardware to see what matches best. In either case, for a stamp option choose 1740. Let me know if you have further questions.

Comparison of the S380 and S385 balance shoes.

Yep! Your old stamp of 17 4 usually corresponds to our 1740 option, which carries 14 through 17 pounds. I feel confident this option will work for you but you can always weigh your sash to verify. As long as it falls in that range then you're good to go.