Which statement about fillet welds is true?

• A. Fillet welds are triangular cross-section joints formed between two surfaces at an angle.
• B. Fillet welds have a throat equal to the weld leg length.
• C. Fillet welds are only used for lap joints.
• D. Fillet welds require a root opening to function.

Answer: (C)

Fillet welds are triangular cross-section welds that form where two members meet at an angle, filling the interior corner along the joint. This triangular profile comes from the two weld legs that run along each member and meet in the corner, creating the weld throat. The throat is the minimum distance through the weld from the root to the face, and for an equal-leg fillet, it is not as long as the leg—it's smaller, about 0.707 times the leg length.

Fillet welds are versatile and used in many joint configurations, not just lap joints; they are common on tee joints and butt joints as well, depending on fit-up and access. They do not require a root opening to function, which distinguishes them from groove welds that rely on a root gap.