20" spiral balancers

Hello. The spiral balance you need depends heavily on the diameter of the tube. If yours measures 5/8", which I suspect it is, you'll need the S500-20 and 17-012 bracket to anchor the balance to the window sash. It also looks like the colored tip that should be at the end of the balance is missing, so you'll need to weigh the window sash and follow the chart under the product description to choose between the blue and red strength options. Thank you!