spiral balance

Hello,

We can't be sure without seeing the end of the spiral but the (3/8") S900 or (5/8") S600 spiral balances would be a good place to start depending on the diameter of the housing tube. There should also be a colored tip at the base of the tube. If not, there is a chart on the product page that explains how to choose your option based on the sash weight. Take a look and let us know if you need anything else. Thank you! 

How to measure the tube length of the S600 spiral balance.