What is the minimum diameter of a plug weld?

The minimum diameter of a plug weld is determined by the need to ensure adequate strength and soundness of the weld while also considering the thickness of the materials being joined. This requirement is established based on the minimum diameter of the weld being equal to the thickness of the plate it penetrates plus an additional increment to account for effective fusion.

Choosing the option that states the minimum diameter is the thickness of the plate plus 5/16" ensures that there is enough material to create a strong connection. This additional allowance allows for processing in environment conditions, tool wear, and variations in material properties, facilitating a robust weld that can adequately withstand stresses.

In this scenario, the other options suggest varying increments of additional diameter but do not meet the established industry standards for minimum weld size. Therefore, the selection of the diameter as the thickness of the plate plus 5/16" reflects a balance between sufficient weld size and practicality in execution.