Balancer tilt double hung 24" long

Thanks for posting. It appears you have a tilt window spiral balance. We can help, but we'll need to clarify a few points. Firstly, the diameter of the spiral balance is determined not by the inner rod, but the outer sheath. The diameter will either be 3/8", indicating you need a Series 900, or 5/8", which means you need a Series 600. I suspect you have a Series 600, but please confirm to be safe. Assuming the entire rod, up to and not including the colored tip, is 24", then see our S600-24. You then have to choose a color tip option, which designates the weight range the spiral balance can support. It appears you might have a faded blue tip; but to be safe, you can weigh the window sash the spiral balances support. You can use that exact weight to determine which color option you need. 

Finally, if the pivot shoe is exactly 1/2" thick, then it sounds like you might have our 15-046. But these pivot shoes have very precise measurements, sometimes ranging into X/32", so you might want to double-check. You can view our selection of pivot shoes here.