When considering the movement of a helical thread, which term best defines its linear progression per revolution?

The term that best defines the linear progression of a helical thread per revolution is "lead." In the context of helical threads, the lead refers specifically to the distance that the screw moves linearly along its axis for one complete revolution of the screw. This is particularly relevant to the design and function of screws, bolts, and other threaded fasteners, as it establishes how far the fastener will advance with each complete turn.

Lead is an important concept in applications where precise movement is crucial, such as in mechanical systems that require accurate positioning. In contrast, pitch is often confused with lead, but it specifically describes the distance between successive threads. Length of action refers to the length along which a thread can act effectively, and throw typically refers to the total displacement of a part, which is not limited to the context of threads.

Understanding these terms is vital in machine design, as they inform engineers and designers about the functionality and application of threaded components in various mechanisms.