Dimensions were small for a while, so it fitted very well by turning the edge with wood. However, I think that it is good to use it even if the screw hole is slightly larger on the outer side but the opening size is somewhat larger. Because it was not perfect at the current position, because the screw could not hit.
Because of the small opening area, the prescribed amount of ventilation could not be obtained, so we decided not to use it. I think that there is no problem in case of natural ventilation, but it is unsuitable in case of forced ventilation. Design and making are good so I would like to use it according to the application.