Which of the following pairs correctly matches F numbers with their definition?

The choice of filler (rod) as the correct answer is based on the established definitions within welding and metallurgical practices. F numbers are part of a classification system used in welding to describe filler materials, specifically identifying the type of filler metal used in welding processes. Each F number corresponds to a specific type of filler material that can be used in various welding applications.

Filler materials are crucial because they must match or complement the base metals being joined to ensure structural integrity and performance of the welded joint. These materials often have unique properties that make them suited for particular types of base metals, including alloying elements and melting characteristics.

In contrast, base metal refers to the material that is being welded, and while it is essential in the welding process, it does not fall under the classification of F numbers. A weld joint describes the configuration of the welded pieces, including the geometry and position, and is also not classified by F numbers. Weld material, while it can imply the materials used in welding, is not a precise term as it can refer to various components, including base metals and filler materials, without specificity regarding F numbers. Hence, the pairing of filler (rod) with its definition aligns accurately with the purpose and application of F numbers in welding contexts.