Which gauge indicates that a countersink is required in the NAS symbol?

In the context of aerospace assembly, the NAS (National Aerospace Standards) symbol is used to denote the specifications for various types of fasteners and related processes. When it comes to countersinks, the NAS specification outlines the need for certain gauges which help determine whether a countersink is necessary for a specific application.

The gauge that indicates a countersink is required corresponds with a specific dimension or feature of the fastener or assembly in question. In this case, the correct answer highlights that when the gauge shows a need for additional recessing of the fastener head, such as when ensuring that the fastener sits flush with the surface or accommodates a specific angle or depth of the countersink, that gauge label is crucial.

Understanding how various gauges relate to counterboring, countersinking, and the overall assembly process is essential for aerospace mechanics because it directly affects the integrity and safety of the aircraft. The identification of the correct gauge and its requirements is key in adhering to industry standards and ensuring effective assembly practices. As a result, being able to recognize the specific gauge that indicates the need for countersinking helps maintain compliance with the NAS specifications and ensures that assemblies are completed correctly.