The flank of a screw thread is the surface that connects the crest (the top edge) to the root (the bottom of the thread profile). It is the sloped surface that forms the sides of the thread and plays a key role in defining the thread’s profile and geometry.
In a threaded component, the flank is angled relative to the thread’s axis and contributes to the overall shape of the thread. For external threads, like those on a bolt, the flanks are the surfaces that mate with the corresponding internal threads of a nut. For internal threads, like those in a nut, the flanks are the surfaces that engage with the external threads of a bolt.
The flank angle and surface finish are important for ensuring proper thread engagement, load distribution, and smooth operation of threaded connections. Accurate flanks help prevent issues like thread binding or stripping and contribute to the mechanical strength and reliability of the threaded assembly. Flanks must be manufactured to precise tolerances to ensure compatibility and performance in threaded joints.