I have a window balance spring to replace

Thank you for sharing your photos with us, Susan. Your balance looks close to both our S380-28 and S385-28. The difference between these two balances lie within the bottom balance shoe. For the Series 380, the bottom balance shoe measures 1" in depth. As for the Series 385, the bottom shoe measures 1-3/32" in depth. You will need to measure the depth of your shoe, like the diagram below to confirm which balance will be the better match. In your stamping, I am actually seeing "2730". But if it says, 2790 as you mentioned, none our tamp options match up to your weight system. Therefore, you will need to weigh your sash on a bathroom scale and refer to the sash weight chart on the product page. There, you will determine which stamping works best based on your sash weight. 

Alternate view of 15-004

I hope this has answered all of your questions. Please let us know if we can be of any further help. 

Thanks for replying back. Seeing a clearer up close photo of the stamped number, I am able to see the "9" now. My apologies for the confusion. As for weighing the sash, you want to weight the part that can be removed from the window (so basically the part that you pull and push down that opens and closes the window). Once you remove it, you can place it on any bathroom scale. From there, refer to the sash weight chart on the product page to determine the most appropriate option to go with.

Ok. So you want to go with the stamping that accommodates that sash weight. Look below at the sash weight chart to decide on the most appropriate stamp option. 

Stamp Option Sash Weight Range

2710                 5 to 9 lbs

2720                 9 to 13 lbs

2730                13 to 19 lbs

2740                19 to 26 lbs

2750                26 to 30 lbs

2760                30 to 33 lbs

2765                33 to 36 lbs

2770                36 to 39 lbs

Great. Make sure you get back to us and let us know how everything works out for you.

We are happy to hear that everything has worked out. We can assist you with your other window. We are here whenever you are ready.