Tie rods in place. These are M6 threads and they run through the depth of the lower-deck or 'landing module' as I like to call it. I've drilled these without a power pillar, so am pleased that they run generally true.
In a perfect world all those surfaces that they penetrate would have been drilled en-bloc so as to line them up precisely, but then hindsight is a wonderful thing.
These rods will support the upper quadcopter or my 'command module' and enroute they will pass through a stay worn around the pilot's waist that stops them from bowing unduly.