The maximum width of a slot weld equals the material thickness plus how many millimeters?

• A. Thickness of the material welded plus 8 mm
• B. Thickness of the material welded plus 10 mm
• C. Thickness of the material welded plus 12 mm
• D. Thickness of the material welded plus 4 mm

Answer: (C)

In slot welds, the weld width is tied to the plate thickness to ensure there’s enough weld metal to fill the slot and provide proper fusion and strength without creating excessive heat input. The standard sets the maximum slot width as the material thickness plus 12 millimeters. That extra 12 mm gives room for a complete weld bead and adequate root and reinforcement across the joint, helping it carry shear loads reliably. If the slot were wider than this, it could lead to burn-through, distortion, or insufficient weld material. The +12 mm option reflects this balance, whereas smaller allowances would not provide enough weld coverage, and would not meet the standard.