I had trouble with the mating of the main rotor grips,#6, and the arm grips-90, #11. Tolerances are so tight that the arm grips had to be slightly filed to fit properly into the grip slot and for the screw holes to line up. After that everything went together great. Instruction sheet could be better such as explaining at what angle the flybar control arm,#28, should fit on the flybar. I am very impressed with the head otherwise. A detailed explanation of building and setting up the head along with color photos can be seen on RunRyder at: http://www.runryder.com/helicopter/t429018p1/ I am told that the Kasama T-Rex 600 head is assembled the same way. An video of it,s assebbly can be found on HeliFreak.com