What tool is most appropriate for measuring a small root gap in a groove weld during inspection?

• A. Micrometer
• B. Caliper
• C. Tape measure
• D. Feeler gauge

Answer: (D)

Measuring a small root gap in a groove weld requires a tool that can fit into the narrow opening with enough resolution to read the exact thickness. A feeler gauge fits that need perfectly: it’s a set of blades of known thicknesses that you slide into the gap until one blade just fits with a light drag. The thickness of that blade gives you the gap size, and you can compare it to the weld specification to verify tolerance. While a micrometer or caliper excels at precise external or internal dimensions, they’re not well suited to probing a recessed, narrow root opening—the geometry makes accurate contact difficult. A tape measure is far too coarse for the small tolerances involved. So, the feeler gauge is the best choice for inspecting a small groove weld root gap.