Sorry about the confusion. The bars are 1/2 inch diameter. I was refering to the actual gap between the bars was 1/2 inch not 1/2 inch measurement from center of bar to the other. Also on the outside of the window I am making a rail 4 inches out away from the window. I will be able to use this to slide a screen in place or in bad weather I can remove the screen and slide in a sheet of greenhouse grade fiberglass.