Correct Spiral balance

Hello there!

Thanks for reaching out to us. It looks like you have a tilt window spiral balance. With that in mind, I recommend the 3/8" Series 900 or 5/8" Series 600 depending on the outer tube diameter. I'm just not sure what heavy-duty balances you're referring to. Can you clarify? 

If you wanted to replace the pivot shoes as well, we would need to see an undamaged version removed from the window track along with the written-out thickness and width. 

In that case, you'd want the Series 900. You will also need to refer to the tip color on your old balance to determine the proper strength option. 

That's odd, no 3/8" diameter spiral balance was ever made with a black tip. The only spiral balance made with a black tip option is 9/16" in diameter (5/8") in the trade. We recommend triple-checking this measurement just to be safe. Be sure to measure only the outer metal tube, you don't want to measure just the bare spring.