This is a fun little design I've perfected over several iterations. Print with supports. I think PLA works best. For some reason the files saved with the propeller angled sideways. make sure to position the file so that the central hole is pointing up and the entire length of the propeller is touching the bed (it'll only do this in one position). After printing, glue a chopstick into the central hole of the propeller with hot glue or something else. All chopsticks are made differently so you might not find one that fits just right. The file "Propeller 4" is the most updated version and works the best. Once you have the chopstick in, spin it between your hands and let it fly!