ToughGrade TG-38 RV ATV Cycle Truck Cargo Work Trailer Side Air Vents This is for a (Black) Two Piece Side Wall Air Vent. Comes as shown in pictures. This vent is designed to scoop air from the outside by using the wedge shaped outer piece and circulate it through the round inside vent into the trailer. The outside piece measures about 8" by 6" and the flange diameter on the round piece is about 4 1/4". The installation requires about a 3" diameter round hole.