Use as many of these as needed when the wall, for any reason, is too thick causing the mounting plate and finished plate to not meet. Longer screws will be needed as well. It adds 3/4 of an inch to the cover plate. If that is too much you can cut to size.
DIAMETERS: Large end inner is 1 5/8", outer is 1 7/8". Small end inner is 1 1/2", outer is 1 5/8".