The anemometer is a simple sensor. 

3 cups are rotating into the wind and a hall sensor counts the turns !

The cups are fixed with a 4mm screw that you will have to trim a the right dimension for the magnet to fly in front of the hall sensor.

On this picture the top nut is inserted into the 3D printed part using the now classical "color change" method !

The hall sensor is kept in place into the 20mm PVC pipe.