Filler metals, also known as welding rods or welding wires, are a material used to join two pieces of metal together during welding or brazing. Filler metals are typically made of the same or similar metals as the workpiece being joined, although they can also be made of alloys that have desirable properties for the specific welding application. The filler metal is melted and fused with the workpiece through the application of heat, and as it cools, it forms a strong bond between the two pieces of metal. The selection of the right filler metal is important to ensure a high-quality weld that meets the required strength and other performance criteria.