Front Sprocket Nut

[limax2]

So I've got my upgraded nut and it is the right thickness overall, but I wasn't expecting it to be hollowed out in the middle making the thread thickness basically the same as a 9 mm nut. Is this right?

Look at the drawing I posted earlier in this thread. You will see the following.
The 12mm nut is hollowed out 1mm more than the 9mm nut, but when fitted this is all in the are of the undercut on the shaft thread so doesn't effect the thread engagement. On the 9mm nut the nut thread overlaps the shaft thread slightly where the shaft is undercut. 
At the outside end the 12mm nut comes to the end of the shaft whereas the 9mm stops short. so you gain about 2mm to 3mm thread engagement above the original approx. 5mm engagement.