Which term describes the deepest point of fusion into the joint?

• A. Toe
• B. Cap
• C. Crater
• D. Root

Answer: (D)

The deepest point of fusion into the joint is called the root. This is the part of the weld that fuses most deeply with the base metals, typically at the bottom of a groove or through the thickness in a butt joint. The root indicates how far the weld has penetrated into the joint, which is crucial for structural strength and integrity. In GTAW, achieving a proper root fusion means controlling heat input, travel speed, and joint fit-up so the weld fully fuses the metals at the deepest point. By contrast, the edge where the bead meets the base metal is the toe, the top surface ridge is the cap, and the end of the weld where welding stops is the crater.