Hello Alan, yes the rod that goes across the fuselage rear has a flat milled on it, I was concerned that everything could slip round but all three horns have a D section moulded into the bore. The worst that could happen if the centre horn grub screw did come loose is that it could move from side to side but not disconnect. Likewise the two outer horns, and on these the self tapping screw goes right through the shaft and is visible for checking.
This system is quite clever because if it's installed with a bit of thought the servo actually pulls for up elevator rather than the normal push for up which I think is the idea of it...
One mod I did do though, did away with the closed loop and used a carbon tube instead, don't mind on rudder but would not trust a crimp on a crucial control surface!
Maybe I'm too cautious but better safe than sorry!
Gary.