This vent cover is designed to fit in any standard 16 by 8 inch opening. The vent cover mounts from the outside and tightens in place with four screws. This vent cover has a solid back to keep air flow blocked from the outside. Often in creating a cross circulation of air, it can be beneficial to block vents to make sure that the air flows all the way across the crawlspace. Additionally, vent openings that are under decks and porches are often a great source of moisture in the crawlspace and it is generally recommended to block those off. These vent covers will match the vent covers used in our 145 CFM Double Fans with Vent Cover. It also has the same look as the Grilled Open Vent Cover.