The standard specifies the dimensions for thread run-outs (where the thread dies out) and thread undercuts (a small groove designed to allow a thread cutting tool to exit) for both external and internal ISO metric threads (DIN 13-1). DIN 76 Type A (Normal Design)

Sharp corners create stress concentrations that cause fatigue failure. A properly machined DIN 76-A radius distributes mechanical stress smoothly across the transition.

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) of the metric thread. The standard provides precise metrics for three primary features: : The reduced diameter of the groove. Undercut Width ( ) : The total width of the relief groove. Transition Radius (

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The DIN 76 standard is divided into four primary forms: .

During lathe operations, the cutting tool needs a "run-out zone" to safely exit the material without colliding with the shoulder of the workpiece.

Without an undercut, a mating part (like a nut) would hit the incomplete "run-out" threads at the end of the screw, preventing it from tightening flush against the shoulder.

The standard provides a system of standardized geometries for the transition area at the end of a thread. This area, whether a gradual run-out or a relieved undercut, is critical for both the manufacturing and functional performance of threaded fasteners.