It allows the bolt head or nut to sit flush against the workpiece.
(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.
DIN 76 is divided into three parts. Part 1 covers metric threads, where the "Form" designations are categorized as follows:
A corrigendum (a minor correction) was issued shortly after the July 2025 version. It corrected a value in Table 1 for pitch P=5.5mm from 3.8mm to 2.8mm for the radius "r". Customers who purchased the previous document received this correction for free, but it's always best to purchase the most current document directly.
The German standard (often searched as DIN 76-A) dictates the dimensions for thread run-outs and thread undercuts for ISO metric threads. Understanding Form A is critical for mechanical engineers, CNC programmers, and machinists. It ensures threaded fasteners assemble smoothly without mechanical interference. din 76-a pdf
These two forms are the core of the standard and represent a significant departure from the related international standard, ISO 4755, which specifies only one type of undercut.
When you open a DIN 76-A PDF table, you will see that the dimensions are entirely dependent on the , rather than the nominal diameter of the screw.
Precise rounding in the undercut helps distribute stress and prevents the fastener from snapping under load. Standard Classifications (Forms A, B, C, D)
When creating technical drawings in CAD software (like SolidWorks, AutoCAD, or Inventor), you do not need to manually draw every curve of the undercut. Instead, standard practice uses a simplified representation accompanied by a leader note pointing to the groove: It allows the bolt head or nut to
In mechanical engineering and manufacturing, precision is the difference between a successful product and a catastrophic failure. When designing threaded components, engineers must account for how threads terminate. This is where the German standard —specifically the Form A (DIN 76-A) specification—becomes critical.
Indicates a shorter thread undercut, utilized only in specific cases where space is severely restricted. 3. Why Download the DIN 76-A PDF?
Standardization documents are protected by copyright and generally must be purchased. You can find the full, current version of at these official retailers: DIN Media (Beuth Verlag): The Official DIN 76-1 Source . Accuris (formerly IHS): Offers DIN 76-1 PDF Downloads .
For full technical data and to ensure compliance with current standards, always refer to the latest DIN 76-A PDF document. DIN 76 is divided into three parts
A sharp 90-degree corner between a thread and a shoulder creates a massive stress concentration point, leading to fatigue failure. DIN 76-A introduces a controlled radius ( ) that distributes stress evenly.
METHOD 1: Thread Run-out (Incomplete Threads) |=========\ <- Tapered profile where cutting tool lifts out | \___________ (Shaft) |==========/ | METHOD 2: DIN 76-A Thread Undercut (Clearance Groove) |=========| <- Sharp thread termination | |___ <- Undercut groove (Diameter < Thread minor diameter) | |________ (Shaft) |=========|___| | 1. Thread Run-out (Auslauf)
The DIN 76-A standard is widely used in Germany and other European countries, and its specifications have been adopted by various industries, including mechanical engineering, automotive, and aerospace.
Understanding this standard is critical for ensuring that threaded fasteners can be fully seated against a mating surface, preventing mechanical interference and ensuring structural integrity. 🛠️ What is DIN 76-A?