What is the surface that connects the crest and roots of a screw thread called?

The surface that connects the crest and roots of a screw thread is known as the flank. The flank is part of the thread profile and plays a crucial role in the performance of the thread, particularly in terms of how well it transmits load and resists wear. The crest refers to the top surface of the screw thread, while the root is the bottom of the thread groove. The flanks are inclined surfaces that connect these two features, and their angle and linear characteristics directly affect the mechanical properties and functional capabilities of the threaded connection.

Understanding the geometry of screw threads is fundamental in machine design, as it influences how threads engage with each other, their load-carrying capacity, and the friction encountered during use. In applications involving assembly and tightening, the dimensions and angles of the flanks are engineered to ensure optimal performance, providing effective resistance to stripping, wear, and other common failure modes associated with threaded fasteners.