It is important to clarify right away that
) of the metric thread. The standard defines specific values for the undercut diameter ( ), the undercut width ( ), and the transition radius ( 1. Undercut Diameter (
DIN 76-1 does not exist in a vacuum. It is part of a family of standards that address similar design features for different thread types. The series includes:
) on every single threaded shoulder—which clutters the drawing—you can simplify the process by using a standard designation callout. You draw the simplified representation of the undercut and point to it with a leader line. Standard Callout Format The text on your drawing leader line should read:
" 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 din 76-a pdf
How to Apply DIN 76-A in CAD Modeling (SolidWorks, Inventor, Creo)
Here are the primary parameters defined in the standard for Form A: 1. Undercut Diameter (
. It is essential for ensuring that fasteners, like bolts and screws, can be screwed flush against a bearing surface and that the thread transitions do not create excessive stress concentrations. BAER Tools Core Purpose and Forms
Note: The transition angle from the undercut diameter back to the thread major diameter or shoulder is typically 30°. How to Call Out DIN 76-A on Technical Drawings It is important to clarify right away that
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 DIN 76-A standard defines crucial dimensions based on the nominal diameter (d₁) and pitch (P) of the thread. Key Dimensions in DIN 76-A
The goal is to ensure that a threaded part can be manufactured (e.g., by turning or grinding) and assembled without interference, while maintaining predictable strength and fit.
Specialized grooving inserts are manufactured specifically to match the It is part of a family of standards
In precision engineering, manufacturing, and fastener design, securing a threaded component perfectly flush against a surface is a recurring challenge. If a bolt thread runs all the way to the head, it can cause stress concentration or prevent a tight seat. This is where comes in.
To ensure you are using the correct and legally binding document, please refer to the official sources below.
If you are a student or hobbyist, a summary table from a textbook will suffice for learning. But if you are a professional engineer or a manufacturing shop, purchase the official DIN 76-1:2016-10 and DIN 76-2:1990-03 PDFs from Beuth Verlag. Consider it a small investment in quality and legal safety.
A typical designation for a thread undercut according to this standard looks like this: