rivet -
heavy pin having a head at one end and the other end being hammered flat after being passed through holes in the pieces that are fastened together
pin a small slender (often pointed) piece of wood or metal used to support or fasten or attach things
rivet -
ornament consisting of a circular rounded protuberance (as on a vault or shield or belt)
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail.