a single 3/8-24 grade 8 bolt holds the prop on our 35 hp 289cc race eng.........I don't think a 10 hp engine will break a 3/8 stud, unless not tightened enough...
If the guys at the field are using wood props the checking is required..The wood compresses and the six bolts loosen and shear off...But not from too much power, just too loose...