Originally Posted by
ThreeIfByAir
In both cases the frame of the door or plug is secured to the aircraft with what appear to be twelve bolts/large screws installed from the inside.
Not being sufficiently familiar with doors, or plugs, like this one, I thought the same thing at first. But those are not bolts or screws, they are "stop fittings and stop pads." The latest video by Chris Brady answers most of the most relevant questions about the construction of the door plug. It's posted above, most recently at #281.