" represents the nominal major diameter of the external thread (e.g., for an M10 bolt with a 1.5mm pitch, Why You Need a DIN 76-A Undercut 1. Ensures Flush Assembly
The transition area where the thread depth gradually decreases to zero.
Short thread undercut. Used when space is limited and the shaft shoulder cannot accommodate a wide groove. It requires tighter manufacturing tolerances. DIN 76-C: Shallow thread undercut.
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For those who need more than just a definition, it is helpful to understand the standard's key specifications. Here is a breakdown of its crucial elements, which are clearly laid out in the tables and drawings of the official PDF. din 76-a pdf
Standards are periodically revised. DIN 76-1:2025-10 is the current, most up‑to‑date version that supersedes all earlier editions, such as the 2016-08 version. The publication history shows multiple revisions in quick succession (2024-11, 2025-07, 2025-10). These rapid updates address editorial corrections and minor technical improvements. Always refer to the latest version to ensure your design uses current specifications.
Sharp corners in mechanical parts act as "stress risers" where cracks can easily form under tension or vibration. The controlled transition radius (
This is the official source for all DIN standards.
): The machined diameter of the relief groove. It is calculated by subtracting a specific factor from the nominal thread diameter ( ). Formula: is a standard-defined depth variable). Groove Width ( " represents the nominal major diameter of the
Once you have the PDF, you will have at your fingertips exactly the dimensions that German and European industry have relied on for nearly a century – from the first edition in 1924 to the current 2016 revision.
Form A undercuts provide a "run-out" zone at the end of a thread. This allows a mating part (like a nut) to be screwed flush against a bearing face and provides clearance for the threading tool (lathe tool or die). Feature Form A (Normal/Long) External ISO Metric Threads (DIN 13-1) Depth ( ) Approx. (Pitch) Length ( ) Approx. Transition Radius ( ) Approx. Angle Usually 30∘30 raised to the composed with power or 45∘45 raised to the composed with power lead-in 3. Sample Dimensions for DIN 76-A (Metric Coarse)
Standard DIN undercuts typically use blend angles of 30 or 60 degrees . Add a thread undercut - PTC Support Portal
DIN 76 is a overarching standard developed by the Deutsches Institut für Normung (German Institute for Standardization). It specifies the shapes and dimensions of thread run-outs, thread undercuts, and thread ends for fasteners with various thread profiles. The standard is divided into several parts and forms: Specifies ISO metric threads. Used when space is limited and the shaft
In the technical diagrams found in these PDFs,
When a thread is machined using traditional turning or rolling methods, the tool cannot stop instantly. As the tool lifts away from the workpiece, it leaves behind a section of incomplete or shallow threads. This zone is called the thread run-out. If a mating nut attempts to flush up against the shoulder, it will jam on these incomplete threads, leaving an unwanted gap. 2. Thread Undercut (Freistich)
Without a DIN 76-A undercut, a matching female component (like a nut or a tapped hole) cannot seat flush against the shoulder, leading to weak joints and assembly failures. Geometric Features of DIN 76-A
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