It was common practice to mount glass shades onto a gallery and was a tradition that began with gas lights. They served 2 purposes. They enabled secure mounting of the shade to the bulbholder and, more importantly, they allowed the heat generated by the light bulb to escape and not overheat the electrical parts. They were available in 3 sizes - 2¼in, 3¼in and 4¼in and ours are available in polished brass, antiqued brass and chromium plate.