Basic paper fastener (6)
I believe the answer is:
staple
This clue is a double definition.
'basic' is the first definition.
(I know that basic can be written as staple)
'paper fastener' is the second definition.
(staple is a kind of paper fastener)
(Other definitions for staple that I've seen before include "office item" , "Paper fastening" , "Chief - paper fastener" , "Basic sort of plates" , "essential" .)