Can't figure out what balance I need

Thanks for posting, Michael. Can you confirm the length of the metal channel? If it's 28-1/2" long, it will have to be specially made. Can you also confirm what the stamp reads? Finally, for the top sash guide, see our 18-171 18-180. This looks like a match.

Thanks for getting back to us. First, I wanted to make a correction to my last post: I suggested the 18-171, but that was in error. I meant to suggest our 18-180. If you look over our pictures, I think you'll agree it's a better match.

As for the stamp, it's usually stamped on the face of the balance by the shoe. Sometimes it wears off over the years, so if you don't have one then you will need to weigh your sash on a scale to confirm the best match. I think your balance is a good match for our S380-29, so if you look at that store page you'll see a chart under the pictures that tells you how much weigh each option can support. Ordinarily you'd just match the stamp to our options, but in your case you'll have to match the weight to whatever range covers it.