Hello I think this is a spring balance for my single hung window.

Thanks for posting, Caryl. You won't be able to order by stamp, you have to choose the Series first. The Series is determined by the combination of nylon fittings so you'll need to figure that out before you go forward with anything.

Based on your photos, I believe that you have either our S390-29 or S351-29. The only difference between these two products is the depth of the bottom shoe, so you'll need to measure yours to confirm the better choice. We have detailed dimensions on each part's store page that you can use as a reference.