Here's some info on Necchi handwheels.
http://www.mckennalinn.com/necchi-no...handwheel.html Yours looks a little different but on this one the clutch washer does come off before the hand wheel. You might have to use a bit of penetrating oil and add some heat or let it sit overnight. Be sure to check the rest of the article. She mentions an oil wick in the hand wheel. I don't know, but yours might have that too and it would be good to know before you think it's a wad of thread and try to pull it out.