Walkera Dragonfly 4 - Page 64

Replace the swashplate and it rests on top of it. Replacing the head now and pressing it
downward onto the shaft, the lower end should butt against the swashplate ball and
now there should be no up/down slop of the swashplate on the shaft. This mod with the
brass ball is what gives you precise control and is essential, probably above any other
in this chapter!