What must be verified using a mandrel gauge?

A mandrel gauge is specifically designed to verify the tolerance of a mandrel, which is a cylindrical tool or fixture used to support or shape a workpiece during manufacturing processes. This measurement is crucial because it ensures that the mandrel is within specified tolerances, which in turn affects the performance and fit of components in an assembly. Proper verification of mandrel tolerance ensures that parts are produced to the required dimensions and specifications, thereby maintaining quality in aerospace applications where precision is critical.

The other options pertain to different aspects of manufacturing and inspection. Rivet head dimensions are typically checked using other types of gauges designed specifically for fasteners. Material hardness can be assessed using hardness testers, and the diameter of fastener holes would be evaluated using calipers or other tools designed to measure hole dimensions. Each of these processes utilizes specific tools and techniques, which are distinct from the primary function of a mandrel gauge.