Arivetis a permanent mechanicalfastener. Before being installed, a rivet consists of a smoothcylindricalshaft with a head on one end. The end opposite the head is called thetail. On installation, the rivet is placed in a punched or drilled hole, and the tail isupsetorbucked(i.e., deformed), so that it expands to about 1.5 times the original shaft diameter, holding the rivet in place. In other words, the pounding or pulling creates a new "head" on the tail 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 thefactory headand the deformed end is called theshop heador buck-tail.