The Moki 180 and I assume the 210 have a prop shaft that is ~12mm in diameter. The front part of the shaft is threaded with a 10mm thread -- the threading process reduced the overall diameter of the threaded portion to 10mm.

If you ream a prop to 10mm it will fit over the threaded portion of the shaft but will not fit over the rest of the 12mm shaft, which is about a 1/8-1/4" in length.

What I did with my break-in prop (I have not installed my Tru-Turn spinner yet, which would just about cover the length of the unthreaded shaft) is to ream the prop for 10mm and ream only through the back half of the prop for 12mm. This gives me a good snug fit for the prop. When I install the spinner back plate I will pay close attention to the length of the unthreaded shaft that still shows and carefully ream only the portion of the prop that will slide over it. You don't want to ream the entire prop for the unthreaded diameter because it will not fit over the front of the shaft snuggly -- potential for the prop to become highly unbalanced.

BTW, this is the only engine for which I have seen this problem -- usually the shaft is threaded from its original diameter which would make the threaded portion of the shaft the same diameter as the unthreaded portion.