Hi all
My Twopence worth the order of fitting is
Shaft , Washer , Nut ( to be used as lock nut on to Prop. ) Prop. A small bit of "Thread Lock2 can be used on the prop threads"
Prop Fitted OK ,

Motor end Fitting , Shaft in Prop tube ( with tube lubed up ) Fitting order , Washer , Nut , ( to lock on Coupling )
Tighten nut down shaft with fingers till firm , slacken back to give some end float ( play in shaft .5mm / 20 Thou ) . Holding nut fit coupling .
Job dun

Timo2
P.S.
You adjust shaft end float if to much by adding 1or2 washer at motor end