spiral balance fastener
Thanks for posting. This depends on the length of the screws used with your old balance, and can vary quite a bit. We carry quite a bit of screws and fasteners here, but can't say for sure which one you need. You can always reuse the screw that mounted your old spiral balance; if you don't have the old screw, we recommend taking one from the other side of the window, or from an identical window in the house, and going to a hardware store to get it matched up with screws of the same size.
Ah yes, I recognize this old thing. I don't know if these types of fasteners are available anymore. They were common back when wood window sashes were popular. If your local hardware store does not carry them, you can also try using a pan head screw like the 33-021 as a replacement.