: Providing a "thread relief" (undercut) so that lathe tools or dies can stop without crashing into the workpiece shoulder.
: The diameter of the relief groove must be larger than the nominal diameter of the internal thread to ensure the mating bolt doesn't bottom out prematurely. din 76-1 pdf
: Allowing a threaded part to be screwed fully into a hole or up to a shoulder without interference from the unthreaded transition zone. : Providing a "thread relief" (undercut) so that
If you're looking for a free version, I couldn't find any publicly available PDF of DIN 76-1. However, some engineering or manufacturing websites might provide summaries, extracts, or interpretations of the standard. If you're looking for a free version, I
Note: Values are approximate and for illustration purposes. Always consult the current standard for design data.
The "run-out" is the length of the incomplete thread. This is the section where the thread depth gradually decreases to zero. DIN 76-1 recommends a specific length $x$ to ensure a smooth transition.