Definition
Metal rods of a specified alloy and diameter that are melted into a weld joint to add material to the molten pool, building up the joint and bonding the base metals together. The rod's composition is matched to the metals being welded (e.g., steel, aluminum, magnesium) so the finished weld has the correct strength and characteristics.
Plain English
Thin metal sticks that a welder melts into a joint to add the metal needed to fill and bond the seam.
Context Anchor
Seen in aircraft maintenance and repair discussions, especially when metal aircraft parts are being welded.
Derivation
From 'filler' (something used to fill a space) and 'rod' (a straight, slender piece of material). The name describes the function: a rod that fills the gap in a weld.
Why Pilots Care
Correct filler rods produce welds that meet strength and corrosion-resistance requirements, preserving airworthiness after repairs.
Intuition Check
Do not read “filler” as anything related to fuel filling or topping off a container. Here it means added metal that fills a joint during welding.
Example Sentence 1
The mechanic selected the correct filler rods for welding the steel engine mount, ensuring the repair would meet aircraft strength requirements.
Example Sentence 2
Using mismatched filler rods on stainless steel can create brittle joints that fail under vibration.