From The Jargon File (version 4.4.7, 29 Dec 2003) :
propeller head
n.
Used by hackers, this is syn. with geek. Non-hackers sometimes use it to
describe all techies. Prob. derives from SF fandom's tradition (originally
invented by old-time fan Ray Faraday Nelson) of propeller beanies as
fannish insignia (though nobody actually wears them except as a joke).
From The Free On-line Dictionary of Computing (30 December 2018) :
propeller head
Used by hackers, this is synonym with computer
geek. Non-hackers sometimes use it to describe all techies.
Probably derives from SF fandom's tradition (originally
invented by old-time fan Ray Faraday Nelson) of propeller
beanies as fannish insignia (though nobody actually wears them
except as a joke).
[{Jargon File]
(1995-01-18)