Metal fixing (4)
(Other definitions for rivet that I've seen before include "Pin for joining metal" , "join together" , "Metal bolt that's hammered" , "fix" , "Completely engross; pin" .)
(Other definitions for nail that I've seen before include "Apprehend" , "What one has at one's fingertips" , "Hit this on the head to be bang on" , "'For want of a . . . . the shoe was lost'" , "Expose as a lie" .)