Quoted By:
Don't listen to the anon who's saying you need to turn the TitanMaster's head around in order to fit them onto the robot bodies properly. He's wrong.
The back of the minifigure heads have grooves in them that the robot body necks are designed to slot into. For example, if you turn the TitanMaster's heads around they can't even stay on Scourge's body.
Pic related.