Vinyl Window Balance

Is there any outer plastic sheathing that had been around that spiral tube still intact? I ask because that's the best way to measure the diameter, not the spiral rod itself. Please check the other balance in this window, or an identical window in the house. If the balance indeed is 3/8" in diameter, then see our S900-28. If it's 5/8" though, you'll need the S600-28. 

For the color, yours might be yellow but to be honest it looks a bit faded--yellow tips usually really stand out and are bright. I advise weighing the window sash. You can then match that exact weight with one of the weight ranges listed alongside each color tip option on the balance shop page.