An Uno fitter sits atop the light socket, and then the bulb is screwed into the socket, holding the shade in place. This is a typical fitter on some desk lamps and floor lamps. Some floor lamps require "THREADED" uno fitters. If your shade requires an uno fitter which screws on to the base of your floor lamp socket, make sure to specify that you need a THREADED uno. The inner dimension of an uno fitter is 1 1/4".