Window counter weight

Hello there. This looks like the 15-087 Coil Balance Shoe and 15-086 Tandem Housing. This setup uses Series 180 Coil Balances. To know what spring weight to select for a replacement coil, look for a stamp on the coil itself, usually near the tongue. If there is none or you're unsure, give me the exact weight of the window sash that these coil springs support, and I can work out what you need.

Series 180 coil balance diagram