When welding to members of dissimilar thickness, the fillet size should not exceed which member's thickness unless calculated stress requires larger?

• A. The thickest member
• B. The thinner member
• C. The average thickness
• D. The smallest member, unless calculated stress requires a larger weld

Answer: (D)

When joining two members that have different thicknesses, the fillet weld size is limited by the thinner member. This ensures the weld reinforcement fits within the edge dimensions of the thinner plate and provides a reliable throat that the thinner part can actually support without causing distortion, burn-through, or overbuild on the light member. In practice, you size the fillet weld to the thickness of the smaller member so the weld can be fully embedded and properly fused on both sides.

If a structural analysis or stress calculation indicates the joint must carry more load, then a larger weld may be justified and required by the design. But absent those calculations, the safe, standard rule is to keep the fillet weld size to the thickness of the smallest member.