This is a base for bird scatter on 18 mm diameter pole.  Use the extended version, or try and put the pivot point at the center of gravity, if you can find it.  

I used several parts form https://www.printables.com/model/155166-birds-scarer-effaroucheur-oiseaux-tic-tic-tic , but I also used portions of a similar model found here:  https://www.thingiverse.com/thing:950635 

You can also find my remix of the rotor blades and prop assembly here:  https://www.printables.com/model/218944-updated-prop-assembly-for-birds-scarer 

I also used the nut and bolt from the following model for my design:  https://www.printables.com/model/194217-m7x20-bolt-screw