Ahh ive done a search and found some information
With Octura props, the X series (an X before the number) indicates a low lift prop. Props without the X are high lift props.
Ex.: X470 Octura prop
X= low lift prop.
4= pitch ratio
70= 70 mm diameter
1667 Octura prop
lift prop
1.6 AR
67mm diameter
So: pitch divided by diameter= (AR) or pitch/67=1.6 or pitch=1.6 x 67= 107.2 mm diameter or 4,2"
Taken from here!!!
http://www.rcprops.com/TechNotes/rcprop_tech_info.htm