Well, dude. If the manual says the NUT is a 10mm nut, you will use a 10mm socket on that badboy.

Now, it's entirely possible the manual is talking about the BOLT and not the nut and the nut is a different size.

Either that, or someone fhucked with your shiz before and put the wrong size nut on there. Well, not wrong; just different size.

"Little, 14mm, different".