Nice duct !
We have ordered and received two props identical to yours. I thought that we could screw tightly the prop to the shaft, but the prop is not adapted for that. It looks like the prop only holds thanks to the pin breaker or whatever you call it. I am puzzled because breaking the breaker would then allow the propeller to escape.
So Silvio did you find a trick to prevent the prop from escaping if the breaker pin breaks ?