RV and Home Brown Stamped Steel Floor Diffuser/Register with Damper 12" X 2" (Duct Opening Size) Outside Dimension 13.5"x 3.75" The Listed size 10"x 10"is

The Listed size 10"x 10"is for inside duct opening measurement

The listed size 6" x 4" is for the inside duct opening measurement

If your duct opening size is 12” x 8”

you will get a large one and it will not fit

Actual outside measurement is 14" x 12"

RV and Home Brown Stamped Steel Floor Diffuser/Register with Damper 12" X 2" (Duct Opening Size) Outside Dimension 13.5"x 3.75" The Listed size 10"x 10"isThe Listed size 12"x 2" is for inside duct opening measurement, actual outside dimension is 13. 5"x 3. 75" Butterfly damper with easy foot operated control dial for desired air flow Two sunk screw holes located at both sides of the register for ceiling and wall mounting with included screws Brown powder coating with matte finish Individually shrink wrapped with card board pad in the back for extra protection