What is the maximum diameter of hole for a plug weld?

What is the maximum diameter of hole for a plug weld?

• A. Thickness of the part plus 12 mm (7/16")
• B. Thickness of the part plus 12 mm (7/16") or 2 1/4 times the thickness of the part
• C. 2 1/4 times the thickness of the part
• D. Thickness plus 16 mm

Answer: (B)

The size of the hole for a plug weld is limited to keep enough surrounding metal for strength while still allowing proper fusion. There are two practical limits: the hole cannot be larger than the thickness of the part plus 7/16 inch, and it also cannot exceed 2.25 times the part thickness. In practice you use whichever of these two values is smaller. This means for very thin parts, 2.25 × thickness may be smaller than thickness plus 7/16 inch, so that smaller value governs. For thicker parts, the thickness plus 7/16 inch becomes the controlling limit. For example, with a 1/4 inch thick part, 2.25 × t is 9/16 inch, whereas t + 7/16 is 11/16 inch, so the plug weld hole must be no larger than 9/16 inch. With a 3/8 inch thick part, 2.25 × t is about 27/32 inch, while t + 7/16 is 13/16 inch, so the 13/16 inch limit applies. That’s why the correct guidance lists both options: the maximum hole diameter is the smaller of these two values.

The size of the hole for a plug weld is limited to keep enough surrounding metal for strength while still allowing proper fusion. There are two practical limits: the hole cannot be larger than the thickness of the part plus 7/16 inch, and it also cannot exceed 2.25 times the part thickness. In practice you use whichever of these two values is smaller.

This means for very thin parts, 2.25 × thickness may be smaller than thickness plus 7/16 inch, so that smaller value governs. For thicker parts, the thickness plus 7/16 inch becomes the controlling limit. For example, with a 1/4 inch thick part, 2.25 × t is 9/16 inch, whereas t + 7/16 is 11/16 inch, so the plug weld hole must be no larger than 9/16 inch. With a 3/8 inch thick part, 2.25 × t is about 27/32 inch, while t + 7/16 is 13/16 inch, so the 13/16 inch limit applies.

That’s why the correct guidance lists both options: the maximum hole diameter is the smaller of these two values.