Which of the following is NOT one of the rules about fasteners?

The correct answer highlights that "No more than 15%" is not a specific rule related to fasteners on the aircraft. In the context of aircraft maintenance and safety, specific guidelines dictate the presence and condition of fasteners to ensure that panels and critical components are securely fastened, which is essential for the safety and performance of the aircraft.

Fasteners play a vital role in maintaining the integrity of structural components. The other options focus on specific locations where missing fasteners could have significant implications for safety and aerodynamics. For example, having no missing fasteners at corners or leading edges is crucial because these areas are subject to various stresses during flight, and any missing fasteners could lead to airflow issues or structural weaknesses.

In contrast, the statement about a percentage such as "No more than 15%" is vague and does not specify a direct safety rule regarding the number or condition of fasteners, thereby making it the odd one out. The emphasis on specific locations indicates precise requirements that are much clearer and direct in maintaining aircraft safety.