I designed this spinner hub to accept folding blades with a 8mm root. The blades are fastened to the hub with two M3 machine screws and nuts.
It all fits like a glove with very close tolerances and did not need any post printing finishing of the part or the holes with my printer and settings.
I designed this to accept the spinner cone that came with the model.
WARNING - THIS PART HAS NOT BEEN SUBJECT TO ANY STRESS ANALYSIS. USE AT YOUR OWN RISK (See comments)
I used supports for the screw holes. I don't think this is really required and would be grateful of some feedback, if somebody prints without supports.