Which dimension is measured to determine the size of a concave fillet weld?

The throat dimension is essential in determining the size of a concave fillet weld because it represents the shortest distance from the root of the weld to the face of the weld. This measurement is critical as it directly influences the weld's strength and its ability to resist forces acting on the joint. The throat is a geometric parameter that helps in assessing whether the weld is adequately sized to meet engineering requirements.

In welding applications, especially for concave fillet welds, the throat dimension is also used to calculate the effective strength of the weld. The other dimensions and factors mentioned in the choices do not provide the same direct information about the weld’s structural integrity or load-bearing capability. Therefore, understanding and accurately measuring the throat dimension is crucial for ensuring the weld meets the specifications set forth in engineering standards and codes.