bucktail

The tail of a deer, traditionally used as a fishing lure.

The end of a rivet opposite the factory head, which in a solid rivet may be bucked by holding a heavy bucking bar or similar-purposed tool against it, while the factory head is hammered until the bucktail is upset into an appropriate shape, most commonly pancake-shaped; the mandrel of a blind rivet generally upsets the bucktail into a doughnut-shape when it is pulled.