22" sash with spring and string

Thanks for posting. This is actually called a channel balance, the spring-loaded mechanism that regulates the opening and closing of the window. The sash is the movable part of the frame with glass. At any rate, we may be able to replace this balance for you, but I'll need just a little more information. Can you show us a picture of whatever clip, hook, or attachment is at the end of that string? Can you also show us how the top of the balance attaches to the top of the jamb track? For instance, does it use a screw, or does it use a hook or s-clip? From there we'll see if we can narrow this down.

It's a huge help, thank you. Based on these new photos, I think you have a match for our S770-22 channel balance. This has the same terminal clip at the end of the cord as your original and is designed to screw in at the top of the window. 

The only point of doubt I have is in regards to the stamp. Your old marking reads "21E" at the tail end, which I believe corresponds to our modern "22E" stamp. You may want to confirm that to be safe, though. Two balances with a 22E stamp carry 24 through 27 pounds. As long as your old sash falls in that range then you should be good to go!