Threaded fasteners (6)
I believe the answer is:
screws
'threaded fasteners' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for screws that I've seen before include "Grooved type of nails" , "Fastner with spiral thread" , "Prisoner guards, colloquially" , "Fastening devices and prison guards, colloquially" , "... men guarding prisoners" .)