window balance

Thanks for posting. This looks like a 15-180 Pivot Shoe, which uses Series 190 Coil Balances. Your old setup used two coils per side and the 15-181 tandem assembly. However, if the window weighs exactly 11 pounds (please double-check to be safe), you could just use just one S190-640 6 pound coil on both sides of the sash. This would equal 12 pounds of support total. So long as you're within one pound of the exact sash weight, that should be fine. You could use the 15-186 Single Support, as well as the 15-182 Balance Bushing. Let me know if you have further questions.