Which balance do I need

Thanks for posting. Thanks for showing us a picture of the pivot shoe, as the identity of the pivot shoe determines the identity of the coil springs you need. Your pivot shoe is actually an older version of our 15-180. This shoe is compatible with our Series 190 Coil Springs. To determine the spring weight you need, look for a stamp number somewhere on the spring itself. If there is no stamp number, or you are uncertain, give us the exact weight of your window sash, and we can work out what you need. Many thanks.

Thanks for getting back to me. If the sash weighs exactly 20 lbs, then I suggest you use (2) of the S190-540 5 lb Coil Springs on either side of the sash. This would equal 10 lbs of support on both sides of the sash, for 20 lbs of support overall. See the 15-181 for a Double Support Detent Clip and the 15-182 Bushing. Let us know if you have any other questions.