counterbalance spring red for window

Thanks for reaching out to us. Can you confirm what kind of window this is? This appears to be a non-tilt window, not tilt. That is a big factor in how these are identified, so please let me know.

Assuming this is a non-tilt window, my first suggestion is the S400-28. This has a 3/8" diameter tube and is a common sight on this kind of window. Just note that it's meant to connect to the sash via hooks at the bottom corners. I don't see such a hook on your sash, but it may just not be something you photographed. 

Just something to keep in mind before you buy anything. If your balance connects to the sash through different means, I need to see it.