The space at the bottom of the joint between the pieces being welded is called the ____.

The space at the bottom of the joint between the pieces being welded is called the ____.

• A. Weld root
• B. Toe
• C. Penetration
• D. Melt through

Answer: (A)

The space at the bottom of the joint where the pieces meet and fuse is the weld root. This region is the starting point of fusion on the far side of a butt joint and forms the bottom boundary of the weld cross-section. It’s distinct from the toe, which is the edge where the weld bead meets the base metal along the sides; from the root, the bead grows upward and outward. Penetration describes how deeply the weld metal fuses into the base metal, not the location of the space itself. Melt-through would mean the weld burns through the far side, creating a hole, which is not what the bottom space is. So the correct term for that bottom-space is the weld root.

The space at the bottom of the joint where the pieces meet and fuse is the weld root. This region is the starting point of fusion on the far side of a butt joint and forms the bottom boundary of the weld cross-section. It’s distinct from the toe, which is the edge where the weld bead meets the base metal along the sides; from the root, the bead grows upward and outward. Penetration describes how deeply the weld metal fuses into the base metal, not the location of the space itself. Melt-through would mean the weld burns through the far side, creating a hole, which is not what the bottom space is. So the correct term for that bottom-space is the weld root.