Window balance problem

Many thanks for your correspondence. Tell us more about the 29" long balance you bought from us. Did it have the same thickness as your old balance tube? Are you able to show us the old balance with a tape ruler next to it? And may we see the top of the window track where the balance is screwed to? From there, we will try and identify what you need. 

Well, I can see one issue right away. It looks like your old balance is longer than the balance you purchased from us. It looks like it's 29-1/2" long; most spiral balances aren't made in 1/2" increments anymore but we usually recommend rounding up to the next highest inch.

It also looks like you have a damaged nylon casing left over at the top of the balance. This is considered the tube, not the rest of the spring you see here. What is the diameter of that white outer casing? If it's 9/16" or 5/8", then you want our Series 600.

The outer tube of our balances serves the same role as that old white casing. The only difference is that ours is metal instead of nylon, since the nylon deteriorates over time. 

They never made a 7/16" balance. If it's less than 1/2", odds are it's 3/8". If that's the case then the Series 900 was correct.

Going back to your first post, you said that the spiral came out of the metal casing. To be more specific, do you mean that when you closed the window, the spiral was yanked out of place as if it were too short?

If so, then going up to the 30" balance should fix this. If you still run into this issue, you could also lower the mounting hole at the top to make up the difference.