In an open butt joint, the gap between pieces equals how much of the metal thickness?

• A. 2 to 3 times
• B. Equal to thickness
• C. 0 to 0.5 times
• D. 0 to 1 times the metal thickness

Answer: (D)

The root gap in an open butt joint is expressed as a fraction of the plate thickness to control how the weld fuses at the root and how the pieces fit together. You want enough space for the molten metal to bridge the joint and achieve root fusion without burning through, while also keeping distortion in check. Allowing the gap from zero (edges flush) up to a gap equal to the full thickness gives the needed flexibility for different material thicknesses and welding conditions with GMAW. A gap much larger than the thickness is hard to weld effectively and can lead to poor fusion, whereas a gap that's too small can hinder root penetration. So the range 0 to 1 times the metal thickness is the right guideline.