Pins for holding two plates of metal together (6)
I believe the answer is:
rivets
'pins for holding two plates of metal together' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rivets that I've seen before include "Metal pins or bolts for holding together two plates of metal" , "Small pins for joining metal sheets" , "Short metal pins" , "Steel pins holding metal sheets together" .)