spirial balance

The company that made your balance system has gone out of business, so this style is no longer available. Fortunately, we have a solution. 

Please see our Series 500 spiral balance for non tilt windows. Based on your size, I'd go with the S500-26. I would also recommend a carrier bracket like our 17-012. This would hook on the end of the S500-26, and also screw to the bottom of your sash. See what you think.

Finally, see our 67-002 screw on face guides. You could use two on each side of the sash to keep it squared in the track when you open and close the window.