Originally posted by ez
Ha ha, not true. You are only seeing the surface in those pictures. Rotors are directional when the internal vanes are not straight, but spiral. The directionality of a rotor actually is not revealed by the holes or slots you see on the outside. i.e. it's the inside that counts :)

This.

Like ez said, the direction of the outer slots means nothing, but the inner vanes mean everything.