Definition
A heavy, hardened steel block held against the protruding shank of a solid rivet to form the shop head as the rivet gun strikes the manufactured head on the opposite side. Bucking bars come in various shapes and weights to suit the rivet size and the access space available on the structure.
Plain English
A small, heavy metal block one technician presses firmly against one end of a rivet while another technician hammers the other end with a rivet gun. The bar's weight and resistance squash the rivet's tail flat against the metal, locking the parts together.
Context Anchor
Used during aircraft sheet-metal repair and assembly, especially when installing solid rivets in skins, frames, ribs, and other metal parts.
Derivation
From 'buck,' meaning to resist or push back against a force. The bar 'bucks' the impact of the rivet gun, providing the solid backing the rivet needs to deform correctly.
Why Pilots Care
Pilots rarely use bucking bars themselves, but understanding how rivets are installed helps when inspecting airframe skins for loose, smoking, or improperly set rivets during preflight or post-maintenance checks.
Analogy
Think of holding a hammer flat against the back of a nail while someone taps the front. The hammer's mass keeps the nail from moving, so each tap shapes the nail rather than just pushing it through. The bucking bar plays that role for a rivet.
Intuition Check
“Bucking” does not mean the tool is jumping or jerking around. Here it means the bar is resisting the driving force so the rivet forms correctly.
Example Sentence 1
The technician selected a smaller bucking bar to reach the rivet inside the tight wing rib bay.
Example Sentence 2
Using the correct bucking bar weight ensures the rivet forms without bending or cracking the skin.