The standard is divided into several "Forms" depending on the application:
Calculated to clear the thread's minor diameter. Radius ( ): Optimized per pitch to balance strength and clearance. DIN 76-A Dimensional Data Table (Reference)
solves this by introducing a precisely engineered groove (undercut) between the thread and the shoulder. This ensures perfect mechanical seating and distributes mechanical stress more evenly. Key Dimensions in a DIN 76-A Technical Data Sheet din 76-a pdf
When looking for an official , it is important to note that the document is officially titled DIN 76-1 ("Tapping holes, thread run-outs and thread undercuts for ISO metric threads"). Tips for Sourcing the Document:
Before diving into the details of Form A, it is helpful to understand where DIN 76‑A fits in the larger family of German thread‑relief standards. The standard is divided into several "Forms" depending
Because DIN standards are copyrighted intellectual property, complete engineering handbooks containing the official DIN 76-1/DIN 76-A standard PDFs must technically be purchased through authorized distributors such as Beuth Verlag or the ISO Store.
For the , the maximum undercut length is specified as ( g_2\max = 3,5P ). In other words, the relief groove is 3.5 times the thread pitch long. The short design (Form B) uses ( g_2\max = 2,5P ) and is reserved for cases where space is extremely limited; it often requires special tooling. 5P ). In other words
The dimensions of a DIN 76-A undercut are directly tied to the pitch (
(Undercut Diameter): The diameter of the groove. For standard metric threads, this is always smaller than the thread's minor diameter ( ) to ensure complete clearance.