Root penetration depth is measured from the top surface of the metal to what feature?

• A. the root face
• B. the filler metal edge
• C. the weld crown
• D. the root bevel

Answer: (A)

Root penetration depth is the vertical distance from the top surface of the base metal down to the root face of the joint. This root face is the boundary at the root where fusion must reach to claim full root fusion, so measuring to this surface provides a consistent reference for how deeply the weld penetrates toward the root. In GTAW, ensuring penetration to the root face indicates proper fusion at the root, which is essential for joint strength. The other features—root bevel, weld crown, and filler metal edge—describe groove geometry, surface height, or filler placement, and do not define the reference depth for root fusion.