I have one window in which the piece broke allowing the window to open, but not stay open (See pictures 0949 and 0950). It appears to be the plastic connection / roller. I have another window in which the spring / coil is not in it's white casing (See pictures 0946, 0947 and 0952). I don't know anything else about these windows, but a friend directed me to your website.
Looks like you have a tilt window spiral balance whose spring came undone. I also spy a broken pivot shoe in your fourth picture.
Concerning the spiral balance, I would wager it's on the skinny side, probably with a 3/8" diameter outer tube. You may want to measure just to be sure. If I'm right, I think our Series 900 will work. You will need the length of the outer tube as well to confirm what size you need.
For the shoe, my first instinct is to go with the 15-045, but this is just an educated guess. I recommend removing yours from the window and comparing its width and thickness to see if it will work. In the meantime, you can see our entire section here.
