GMN Shaft Lock with Hirth Gear/Joint 

2 keyways it seems. A diaphragm could actually be a better solution for torsional rigidity and stiffness

Been a few months, but the other reply is incorrect. If you watch closely there is a ring gear on the spindle and a ring gear on the housing both on the nose side of the assembly (note the diameter of the coupling gear, it is showing exposed teeth beyond the diameter of the spindle ring gear). When the coupling gear is pushed forward by air pressure it contacts the two ring gears locking the spindle to the housing. The pins visible on the back of the coupling gear are to keep it aligned while traveling in and out without it getting cocked and jamming. The flaw in a setup like this is if the two forward ring gears are not perfectly in line axially (one gear proud of the other) the connection will have play.

3 total hirth faces, one wide piston hirth face that moves forward and back, no need to locate, it can rotate free, oppossed is one narrow upper face that is bolted to the housing fixed, the other is narrow aswell and more inner mounted to the spindle shaft, the bog wide piston one links all 3 together or none at all, with all 3 together the two rotating faces, piston and spindle link to housing

with animation like that, who cares. One would assume Magic.