Springs for single hung windows

Thanks for posting. I'm afraid that Series 850 length is no longer made. Fortunately, we have a solution.

We believe you can use our Series 795 channel balance as a replacement. However, there are a couple things you need to keep in mind. The first is the size of the shoe: The Series 795 comes with a 1-1/4" wide shoe by default. If yours is 1-1/4" wide, too, then great! If it's 1" wide, though, you'll need to purchase the 15-194 separately and swap the shoes out when you receive them.

Another detail is the strength of the spring. The Series 795 uses a different rating system than the Series 850. Because of this, you will need to get the exact weight of your sash to confirm the best stamp option.

Finally, there's the pivot bar. The old pivot bar won't work with the new shoe. There are actually a couple different options here, depending on what you have. If your old pivot bar looked like our 26-318, then we recommend using our 26-021 instead. If your pivot bar looked different, though, then let me know. We would need to see a picture of it.

Thanks! Based on your existing pivot bar, I think our 26-021 will work fine. Based on your sash weight, I recommend our 28B option for the S795-28.