Window coil balance need to identify replacement

Hello there. This looks like a 15-177 Pivot Shoe, which uses Series 152 Coil Balances. A Series 152 coil spring stamped 'F' can be replaced with the S152-6 6 pound spring. If your old coil housing is undamaged you can reuse it; otherwise, see the newer style 15-143, 15-144, and 15-145. These components 'sandwich' around the coil spring. Let me know if you have further questions.