The external round vents are chamfered that can help immediate water far from the opening, the internal sq. vents have an integral fly monitor to prevent insects from entering with the vent. The pair of vents lets a move of air through your garage to assist hold out musty smells. https://woodengarage89011.blogminds.com/the-smart-trick-of-garages-preston-that-nobody-is-discussing-25700124