threads where a shorter relief is required for technical reasons. BAER Tools Breakdown of the Standard
DIN 76‑A is not a complete standard by itself. It is a defined inside DIN 76‑1 , the German standard that specifies thread run‑outs and thread undercuts for ISO metric threads.
It creates a groove at the end of a thread that is smaller than the minor diameter of the bolt. This allows a mating part (like a nut) to screw all the way to the shoulder of the bolt without interference from the incomplete threads that occur at the end of a threading tool's path. Dimensions: For Type A, the maximum width of the undercut ( ) is typically is the thread pitch).
Official copies of the DIN 76-1:2016-08 are available through the or authorized distributors like ANSI . For quick technical reference, engineers often use summarized tables found in resources like the Tabellenbuch Metall . AI responses may include mistakes. Learn more Share public link
In technical documentation, you will often see forms A through D: din 76-a pdf
However, it is crucial to stress that the precise, legally valid dimensional data for Form A and Form B is exclusively contained within the official, copyrighted . While third-party websites may host scanned copies, these are generally unauthorized distributions and often subject to copyright infringement [14†L4-L8].
| Thread pitch ( P ) (mm) | Undercut length ( g_2 ) (approx.) | Undercut diameter | Transition radius ( R ) | Relief angle | |--------------------------|--------------------------------------|--------------------|--------------------------|--------------| | 0,2 | 0,7 mm | 0,3 mm | 0,1 | 30° | | 0,25 | 0,9 mm | 0,4 mm | 0,12 | 30° | | 0,3 | 1,05 mm | 0,5 mm | 0,16 | 30° | | 0,35 | 1,2 mm | 0,6 mm | 0,16 | 30° | | 0,4 | 1,4 mm | 0,7 mm | 0,2 | 30° | | 0,5 | 1,75 mm | 0,8 mm | 0,2 | 30° | | 0,6 | 2,1 mm | 1,0 mm | 0,4 | 30° | | 0,7 | 2,45 mm | 1,1 mm | 0,4 | 30° | | 0,75 | 2,6 mm | 1,2 mm | 0,4 | 30° | | 0,8 | 2,8 mm | 1,3 mm | 0,4 | 30° | | 1,0 | 3,5 mm | 1,6 mm | 0,6 | 30° | | 1,25 | 4,4 mm | 2,0 mm | 0,6 | 30° | | 1,5 | 5,2 mm | 2,3 mm | 0,8 | 30° | | 1,75 | 6,1 mm | 2,6 mm | 1,0 | 30° | | 2,0 | 7,0 mm | 3,0 mm | 1,0 | 30° | | 2,5 | 8,7 mm | 3,6 mm | 1,2 | 30° | | 3,0 | 10,5 mm | 4,4 mm | 1,6 | 30° | | 3,5 | 12,0 mm | 5,0 mm | 1,6 | 30° | | 4,0 | 14,0 mm | 5,7 mm | 2,0 | 30° | | 5,0 | 17,5 mm | 7,0 mm | 2,5 | 30° | | 6,0 | 21,0 mm | 8,3 mm | 3,2 | 30° |
: Short undercut for external threads, used when space is limited. Forms C & D : The equivalents for internal threads (tapped holes). Why Use Form A? Flush Seating
: 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 threads where a shorter relief is required for
Understanding DIN 76-A: Thread Run-outs and Undercuts (A Detailed Guide & PDF Resources)
This is the official source for all DIN standards.
: Used for ISO metric threads (coarse and fine pitch) as defined in : The undercut includes a specific radius ( ), a depth ( ), and a width ( ) to ensure structural integrity and proper clearance. Form Comparison
The official current version is . You can access or purchase technical guides and tables from these sources: It creates a groove at the end of
Standard undercut for external threads (normal depth).
If you require the official, fully detailed engineering document for compliance or auditing purposes, you can obtain the official (which covers Form A external threads) directly through the Beuth Verlag website or the Deutsches Institut für Normung (DIN) portal. Many manufacturing and engineering software suites (like SolidWorks, Autodesk Inventor, and McMaster-Carr CAD libraries) also come pre-loaded with DIN 76-A configurations for automatic insertion into designs. If you are working on a specific design, let me know:
(Transition Width): The length of the angled chamfer leading back to the blank shaft diameter.
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