It aligns with, but sometimes differs from, international standards like ISO 3508. 2. Technical Characteristics of DIN 76-A
According to DIN 76, undercuts are categorized into four primary forms: BAER Tools Form A (Long): Standard "normal" design for Form B (Short): threads when space is limited. Form C (Long): Standard design for (tapped hole) threads. Form D (Short):
Here is how to interpret that:
In mechanical engineering and manufacturing, thread run-outs and thread undercuts are critical components of fastener design. (often referred to simply as DIN 76-A) is the definitive German standard that governs the dimensions for metric thread run-outs and thread undercuts for external threads. din 76-a pdf
: It allows the mating component (like a nut or a tapped plate) to screw down completely flush against the bolt shoulder.
: Ensures the underside of a bolt head or a washer sits perfectly flat against the workpiece. Stress Distribution
: Typically applied to internal threads (tapped holes). It aligns with, but sometimes differs from, international
Note: For exact values, always refer to the official tables in the DIN 76-A PDF, as values vary by thread size (M3 to M100+).
When engineers write “DIN 76‑A” on a drawing, they are telling the machinist: manufacture an external thread undercut according to DIN 76‑1, Form A, with the standard normal length . The PDF of the standard contains the exact formulas and tabulated values that determine how deep and how long that undercut must be for a given thread pitch.
As a practical example: for an thread (pitch 1.5 mm), a DIN 76‑A undercut would have an undercut diameter of approximately 2.3 mm (relative to the thread core), a length of about 5.2 mm, and a transition radius of 0.8 mm. Form C (Long): Standard design for (tapped hole) threads
Thread run‑outs and thread undercuts might seem like minor details, but in precision manufacturing they can make the difference between a reliable assembly and a field failure. DIN 76‑A is one of the most widely referenced German fastener standards for ensuring that threaded components seat correctly, tools run safely, and threads meet their specified strength requirements. If you have been searching for a – whether to download the official document, understand its dimensions, or apply the standard in your own designs – this article provides a comprehensive, actionable guide.
DIN 76‑A is ubiquitous in:
The English translation is prepared by the DIN language service; however, the standard notes that “in case of doubt, the German‑language original shall be considered authoritative.”
Guarantees that nuts or mating parts seat perfectly flat against a shaft shoulder.
: By providing a smooth radius in the undercut, it helps distribute mechanical stress, reducing the risk of fatigue failure at the thread-to-shank transition. Standardization