Balancer assembly

This looks like our 15-111 Pivot Shoe, which uses either 1/2" thick Series 160 Coil Balances or the 3/8" thick Series 165 balances. You'll need to measure your existing coil springs to know which you need. If you're unsure of what spring weights to select, obtain the exact weight of the window sash. Give me that exact weight, and we'll work out what you need. 

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Then it sounds like you need the 1/2" Series 160 Coil Balances. I highly advise obtaining a more exact sash weight before proceeding, as you need the spring weights chosen to be as accurate as possible. Lowering the sash onto a bathroom scale should suffice. Give me that exact weight and I'll work out what you need. 

If the window weighs exactly 25 pounds, then I'd use (1) of the S160-6 6.5 pound springs and (1) of the S160-5 5.5 pound springs on each side of the sash. This equals 12 pounds of support on either side, for a total of 24 pounds overall. Being within one pound of the exact sash weight should work fine. For new covers, use our 15-150D. Let me know if you have further questions.