One might be bolted down (3)

I believe the answer is:

nut

(Other definitions for nut that I've seen before include "eccentric type" , "Hard shell of a locking device" , "Hard-skinned fruit" , "eg Hazel" , "Screwball" .)

I've seen this clue in The Wall Street Journal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.