Buck: The bar that shapes rivets, not currency
To buck a rivet means to reshape its tail with a heavy bar, a metalworking sense that came long before the word meant money.
To most people, a buck is a dollar, a male deer, or the act of resisting something. In metalworking, to buck means something altogether different: to hold a shaped steel bar firmly against the tail end of a rivet while the opposite end is struck with a rivet gun, deforming the tail into a final shape, usually a flat pancake or countersink. The person doing this work is called a bucker; the bar itself is a bucking bar. Together they form one half of the rivet closing process, the other half being the strike force of the pneumatic gun.
The bucking bar is heavy, typically made of hardened steel, and must be held in precise contact with the rivet tail throughout the hammer blows. The bar absorbs and redirects the impact energy back into the rivet, upsetting and spreading the tail material outward and flat. Without this counter-pressure, the rivet would bend or shear rather than form a secure head. If the rivet is particularly hard or thick, it may be heated first to soften it, making the metal flow more easily under the bucking bar's pressure. This is foundational work in aircraft assembly, shipbuilding, and boiler fabrication, where riveted joints must be airtight and structurally sound.
The word buck in this sense predates the American slang for a dollar by some time. It likely derives from the bucking action itself: the verb to buck meaning to press or push against something with force, as a horse bucks to throw a rider. The bucking bar pushes back against the rivet; the rivet and bar work in opposition. This metaphor of resistance and counter-pressure makes the name natural and descriptive.
Other industrial terms share this sense of opposition or shaping under force. A buckle, in manufacturing, is a permanent distortion or bend caused by excess pressure or stress, the opposite outcome of a controlled bucking operation. The bucking bar, by contrast, is a tool of precision and control. The bucker's skill lies in holding the bar steady and perpendicular while absorbing repeated impacts, a role that remained common in metalworking shops until modern automated rivet systems reduced demand for the trade.
The dictionary entry
buck
(verb, metalworking)
To press a heavy, shaped bucking bar against the bucktail of a rivet, while the opposite end (the rivet factory head) is hammered by a rivet gun, to upset the bucktail into an appropriate shape, most commonly a pancake-shape.