What does a 4-40 x 1/2 machine screw specification indicate?

The specification "4-40 x 1/2" for a machine screw indicates that the screw has 40 threads per inch, which is represented by the "40" in the specification. The "4" indicates the screw size according to standardized thread size classifications, and the "1/2" indicates the length of the screw, which is half an inch. Therefore, the focus on 40 threads per inch as a key characteristic shows how closely spaced the threads are, affecting the screw's holding power and application. This is particularly important in precise mechanical applications where the grip provided by thread count plays a crucial role in the assembly's integrity.

The other options do not accurately reflect the specifications given. The twist "length" measurement is explicitly stated as 1/2 inch in the specification and does not refer to the diameter, which is not provided in the given specification directly. Thus, focusing on the number of threads specifically illustrates the significance of thread count in mechanical fastening.