Which part of the thread is referred to as the flank?

The flank of a thread is defined as the side of the thread that connects the crest, which is the highest point of the thread, to the root, which is the lowest point where the thread depth is measured. This part is crucial in determining how the thread interacts with a mating thread, particularly in providing strength and stability when the two threads engage. Understanding the flank is important in applications involving fastening, as it plays a role in the friction and load distribution characteristics of the threaded connection.

When examining the other options, the outermost edge of the thread describes the crest, while the root refers specifically to the low point of the thread. The angle formed by the thread profile pertains to the entire geometry of the thread but does not define the flank itself. Hence, the description of the flank accurately represents its location and function within the overall structure of the thread.