Coil spring balance replacement

Question

The spring unit is 4.5 inches long. There are no markings on it. Installed in 2002 when house was built. The coil cover allows the sash spring clip to slide over top of it. If the coil unit is too thick, it will catch on the spring clip and prevent the window from opening.
The sash weight is 21 pounds. The spring unit has broken on several windows and I'm looking for a suitable replacement.
Thank you!

Tom · Accepted Answer

It's very difficult to make out your pivot shoe from these photos, as it is obscured by the sash, but it looks like it might be a match for our 15-199.

If I'm right, then this shoe is compatible with two different sized springs: either the 1/2" Series 160 or the 3/8" Series 165. You will need to remove one of your originals and measure it to confirm the better option.

I personally think you might have the Series 165. If I'm right then you can also use the 15-204 cover. Don't take my word for it, though. You should measure to be safe.