Abstract: A cover for an air vent opening in a building comprising a generally rectangular housing portion have a central panel, side and end walls, and provided with a mounting peripheral flange formed by side and end flanges extending in a plane substantially parallel with the plane of the central panel portion of the vent enclosure part of the cover. The end flanges are provided with keyways having round portions and narrower slot portions through the end flanges along a latching surface in each of the flanges which is an inclined plane providing a flange thickness greater along the slotted than along the round portions of the keyways. The cover is held in place by screws fitting through the keyways and wedged with the latch surfaces on the end flanges of the cover by moving the cover laterally.