Complex joints, typically for jewelry or live steam boilermaking, may be made in stages, with filler metals of progressively lower melting points used in turn.
Many gas welding processes, such as lead burning, are typically autogenous and a separate wire filler rod of the same metal is only added if there is a gap to fill.
With electric arc welding, a major use for the filler rod is as a consumable electrode that also generates heat in the workpiece.
A hard, but more expensive and sometimes brittle, facing alloy is deposited onto the wear surfaces of mild steel tools.
Sometimes non-consumable electrodes are included as well, but since these metals are not consumed by the welding process, they are normally excluded.
Covered electrodes are used extensively in shielded metal arc welding and are a major factor in that method's popularity.