What is the imaginary line formed by the intersection of the flanks of a thread when extended?

The imaginary line formed by the intersection of the flanks of a thread when extended is referred to as the sharp crest. This concept relates to how external threads are designed, where the crest is the topmost point of the thread profile. The sharp crest is significant because it represents the critical area where contact occurs with corresponding threads in a mating component. This line is crucial for understanding the functional aspects of threaded assemblies, such as how they engage and transmit loads.

In contrast, the sharp root is the area where the flanks meet at the bottom of the thread profile, which does not describe the intersection of the flanks. The root apex may refer to a specific geometric point in some contexts, but it does not encapsulate the definition requested. The option of "All of these" incorrectly implies that multiple terms can describe the same imaginary line, which is not accurate. Thus, the definition of the sharp crest is essential for grasping how threaded components interact and function within mechanical assemblies.