On this one I think Win ran a bolt through the prop, it's held on by a nut in the middle.
I've done the same thing in the past with SS bowls, and 3 or 4 wood screws in the lip around the outside of the bowl work nicely.
I've put those on a few wind turbines... but always windup taking them off in the end, I kind of like the look of the flat hub w/bolts sticking out. It's all just a matter of preferance though...