This is an anemometer, a tool for measuring wind speed. The arms of this one are hexagons, so that they can be slotted in and kept in place.

Glue is optional but recommended. If this will be outside in the summer, consider printing it with either…

A strong enough PLA: https://amzn.to/3xSMhol

or ABS: https://amzn.to/3UmcWS8

Thank you to 3DHoJor for donating the filament that I used for this project!

Additionally, the only non-3D printed part you will need is a single 608 skateboard bearing. If you don't already have some lying around, I highly recommend buying some, as many in the maker community use them for a variety of projects: https://amzn.to/4bjiG65