660 Fifth Avenue - Wikipedia The enamel or white glass strips were 20 inches (510 mm) wide and were flanked by 3-inch (76 mm) strips of aluminum, giving the mullions a total width of 26 inches (660 mm). [23] [27] The window widths varied from 6.875 to 7.375 feet (2.096 to 2.248 m). [23]