The attachable mounting flanges covered by this specification are intended to be attached to instruments whose cases conform to the standards specified in column 3 of table I to adapt them for installation in instrument panel cutouts which were made to accommodate instruments whose cases conform to the standard specified in column 4 of table I. A point of the dial of the instrument which should be at the top, bottom, left, or right should be alined with the reference mark on the flange. The thickness of the instrument panel should not exceed 0.125 inch. The instrument may be installed in the panel with the flange either on the front or on the rear of the panel.