We guess that the flex is XH.
At that time (in 2009 for this Gen3), the machine for engraving was quite basic and had not the "X" letter!
Moreover, this Extremecarver Gen3 is seldom, because the XH flex exists now only for Pro2 model.
Note the range of rider's weight for the board size 175: 100-115 kg.
The Swoard team