Spiral window balance

Thanks for posting, Jeff. This looks to me like its either a S600-29 or S900-29. The only difference between these two balance Series is that the Series 600 has an outer tube that is 5/8" in diameter, while for the Series 900 this outer tube is 3/8" in diameter. The outer tube is missing on your balance, so I can't say for sure what your tube's diameter is; however, your balance's colored tip looks blue to me; this option would only be available for the S600-29. If you have an undamaged version of this balance, you ought to measure the diameter of its outer tube just confirm this. Let me know what you find.