Here is a short "technical story" to explain why this standard exists and how it works. The Problem: The "Vanishing" Thread
To fix this, Leo looks up . This standard tells him to cut a small groove (an undercut) at the base of the thread. din 76a pdf
: Fasteners with thread undercuts may not meet the same minimum breaking loads or torque requirements as those with standard run-outs. Here is a short "technical story" to explain