Vintage marked Corning No 820120 Cone Shaped Milk Glass with Waffle Pattern.  Dimensions are 8" Diameter x 5 3/4" Tall with a 2 1/8" Fitter at the bottom.  This is a great replacement glass for your vintage lamp which needs this diffuser.  I had one on my grandmother's standing floor lamp, and Torchiere style table lamps also need these.  Make sure to measure the size you need as there are many different sizes.  The Corning markings are down inside near the neck, in raised letters which I tried to show in the pictures.