After using the open countersink to edge break the first hole, which tool should be used to inspect the edge break?

Using a countersink gauge to inspect the edge break after employing an open countersink is the most appropriate method because this tool is specifically designed to measure the depth and the angle of countersinks accurately. It allows the mechanic to ensure that the edge break meets the required specifications, which is crucial for both safety and functionality in aerospace applications.

A countersink gauge provides a standardized reference to verify that the countersink is adequately formed and that the edge is beveled as intended, reducing the risk of stress concentrations or potential failure due to improperly finished edges.

While calipers and micrometers can measure dimensions, they are not tailored for assessing countersunk angles or the specific profiles of edge breaks, which means they would not provide the precision necessary for ensuring compliance with aerospace standards. Visual inspection alone, albeit useful for general checks, lacks the quantitative assessment needed for critical applications where precision is paramount.