Home craft window coil spring.

Thanks for posting. While this could be a Series 150 Coil Spring, I honestly can't be certain without seeing the 'tongue' of the coil spring or, better yet, the pivot shoe that that tongue attaches to. If you want to be certain, remove the system from the window and show us the springs and pivot shoe. As far as the spring weight goes, I'm also afraid to say that the number on the housing is probably irrelevant to the actual spring strength; that is likely just a patent number for the housing itself. You will need to remove the coil springs and look for stamps on the actual tape. If there are no stamped numbers, weigh your window sash. Give us that exact weight and we'd be happy to figure out what spring weights you need.

Actually, the picture of the pivot shoe is a big help in this case. I recognize what you have: this is an old balance system that is not made anymore, so we can't provide an exact match. That said, I think the Series 140 Coil Balance system might work as a replacement for you. Take a look and see what you think. If the Series 140 does work for you, the convenient thing about them is the coil springs and pivot shoes come as one part. To know what spring weight you need, you'll need to weigh your window sash and divide by two. For instance, if your sash weighed 18 lbs, you'd want the S140-9.

An issue with switching to the Series 140 is that you'll need new pivot bars, as your old ones won't be compatible with the new pivot shoe. You'd want either our 26-398 or 26-405, depending on which one is a match for your current pivot bar's hole spacing. 

Look over all these recommended parts, and let us know what you think.