Learn more: The Uno fitter is threaded so that it screws onto the bottom end of a socket. Down Bridge arm lamps are the most common type of lamp that take a shade with an Uno fitter. Down Bridge arms are typically found on floor lamps, but table lamps can have them as well. They have a top arm which extends off to one side of the central column. Down Bridge arm lamps take a shade that is designed to push the light downward. Top Quality frames and materials.