spiral tilt spring balance

Thanks for posting! This is a bit odd. You mention that your balance is for a tilt window, but your first picture shows a spiral balance specifically designed for non-tilt windows. Then your second picture shows the same non-tilt type spiral balance (top) and then a standard tilt type spiral balance (bottom).

I can't be sure, but I'd wager that your tilt windows were repaired at some point with incorrectly chosen non-tilt spiral balances. Assuming these are, indeed, tilt windows, and that keeping in mind that the outer metal tube is 3/8" in diameter, then I would recommend our Series 900 spiral balance. I would double check the outer diameter, though, just in case. If it's 9/16" or 5/8", go with our Series 600 instead.