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
tail. On installation the rivet is placed in a punched or drilled hole, and the tail is
upset, or
bucked (i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, pounding creates a new "head" on the other end by smashing the "tail" material flatter, resulting in a rivet that is roughly a dumbbell shape. To distinguish between the two ends of the rivet, the original head is called the
factory head and the deformed end is called the
shop head or buck-tail.