The Lego Duplo Helicopter 2616 I found in my old toy box lost its propeller possibly long ago when I was still a kid, so I had to make a replacement part to give it to my niece. It's not having the central upper nub as the original would have, but it works fine to complete the look of the helicopter and make it more playable.

To achieve perfect fit, one might need to drill open the center hub of the print to up to 6mm, depending on damage or deformation of your spoke.