Back around 1960, when I was 12 or 13, I got invited to a very small, very local "science fiction convention", which was a one-day event that mostly consisted of presentations and panel discussions. At the time, young teenage fans were looked down on as being "kids with propeller beanies". So, naturally, I decided I wanted to wear a propeller beanie to the event. I couldn't find one in any store, but they did have plain beanies; I bought a propeller, and the appropriate bearing, from a place that sold model-airplane parts, and attached it to the beanie. Isaac Asimov (!) thought it was "cute" :-)

That propeller was deliberately large, with a diameter nearly as big as the beanie itself. But I'm pretty sure there are some very small propellers available now - say, 3 to 4 centimeters radius... *giggles*