Ok, great - looks like I am going for a Series 351. A couple of more questions for you:
1) I had most of my other channel balances replaced by a 'professional' a few years ago, and ever since it sounds like the springs are scraping or rubbing against the hook when the windows is operated. Does this mean the channel balances might be the wrong size? They all work, but the noise is annoying.
2) Is there an advantage to using a bottom shoe that has the wings over the ones that don't? They seem to have the same dimensions otherwise. Are they interchangeable?
Thanks so much!
Glad we were able to help. I'll address your questions one at a time.
1) There could be a lot of reasons why a balance makes noise when the window opens and closes, but the most common source is a certain type of hook used by some manufacturers. This hook is designed in such a way that it causes the knot in the string to rub against the spring as it operates. Eventually, the knot will fray and the string will snap, and this could actually cause damage to your window. Fortunately, the balances we supply have a bent hook that relieves pressure on the knot and prevents the excess friction.
If you have other windows in the house with this kind of hook and you don't plan on replacing the balances, then there is a quick solution. You could drill a small relief hole in the jamb itself to "cradle" the knot.
2) Nylon balance attachments with wings are specifically meant to stabilize the balance in certain jamb tracks. Since your balances dodn't have wings, I see no problem just sticking with that.