When performing a test plug weld, it should be made on the same type and thickness of metal as that to be welded on the vehicle.

• A. Thickness
• B. Finish
• C. Type
• D. Grade

Answer: (C)

You want the test plug weld to mirror the material you’ll weld on the vehicle because the metal’s chemistry and behavior during welding determine whether the weld will fuse properly, penetrate correctly, and avoid issues like cracking or porosity. The type of metal governs melting points, thermal conductivity, and how the base metal interacts with the filler metal, so matching the metal type ensures the test results reflect what will happen in the actual repair. Thickness matters for heat input and weld size, but it’s the alloy type that most critically controls weld quality and performance. Finish and grade aren’t the primary drivers of how the weld behaves, since they pertain more to appearance or strength within the same material family, not to the metallurgical response of the weld.