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