Double Coil Balance/Brake Shoe
Thanks for posting. This looks like an older version of the 15-177 Pivot Shoe, which works with Series 152 Coil Balance spring sold separately. For new coil covers, see the 15-143, 15-144 and 15-145. These parts sandwich around each individual coil.
For the replacement coil springs you need to choose a spring weight, which reflects the weight each individual coil can support. The "D' stamp might suggest you need a 4 pound spring, the S152-4. But if in doubt, weigh the window sash these balances support. Give me the weight and I can work it out for you.
The weight of the window sash supported by these coils is 29-30 pounds.
If you are certain the window sash weighs between 29 and 30 pounds, you could use the S152-7 7 pound spring and S152-8 8 pound spring, one of each on both sides of the sash. This would give you 15 pounds of support on either side, for a total of 30 pounds of support. Let me know if you have further questions.
