Cover dimension is 3.5" x 2.5". Needed to work through the bottle necked flange that is 2.5" x 1.5"! All work and pictures done upside down on back under wing that is 31" off floor. Before Taco install, gave floxed edge of hole and edge of cover a skim of JB KWIK, and a sand/fitting. Fit is not perfect, can squeeze 1 piece of copy paper, (.0025") in gap, but not 2! After hole is painted, will fit and allow for paint on cover.