I have a screw with a washer. Which one of the two sides should it go through (ie which side the washer should be "in contact with"), the flat or the curved one? The structure is symmetrical so it can go either way. The other side of the frame (opposite to where the washer will be) is going to be mounted to a flat surface. Basically the screw goes through the hole of the metal frame and screws on the flat surface on the other side. If someone also knows the reason why one is more suitable than the other it would be great.