What is the nominal diameter of a standard metric thread with a specified value?

The nominal diameter of a standard metric thread refers to the approximate diameter of the thread, measured in millimeters. In the context of the choices given, a nominal diameter of 10 mm indicates the thread's size and fits within the common specifications for metric threading.

The nominal diameter serves as a key parameter in defining the thread's specifications, including its pitch and profile. A nominal diameter of 10 aligns with frequently used sizes in various applications such as machinery, fasteners, and structural components. Therefore, it is a common choice in design and manufacturing scenarios needing a reliable thread size.

When considering the other values, while they may also represent nominal diameters for different fasteners, 10 mm is a widely utilized standard that matches many threading applications, making it the correct choice for this question.