specification refers to a specific type of thread undercut (Form A) for external ISO metric threads, defined under the broader BAER Tools Understanding DIN 76 Form A According to the standard,

Critique: Some find the DIN 76 series a bit "dry" (as it's mostly tables of millimetre measurements), but its technical accuracy for ISO metric threads (DIN 13-1) is unmatched. Where to Find the Specs

5. Summary of Dimensions (DIN 76-1 Reference)

If you just need the value of $a$ (the width) for a standard metric thread, here is a quick reference table derived from the standard:

If the drawing shows a shaft with a thread ending at a shoulder, the machinist must look up the P (pitch) in the DIN 76-A PDF and machine the undercut to the specified width and depth.

Understanding DIN 76-A PDF: A Comprehensive Guide

Cost: Approximately €80–120 for the PDF (as of 2026).

DIN 76 is the industry-standard blueprint for ensuring that threaded fasteners actually fit together. Specifically, DIN 76-1 deals with thread run-outs and undercuts for ISO metric threads. If you've ever wondered why a bolt doesn't sit perfectly flush against a surface, the answer is likely found in this standard. The "Why" Behind DIN 76

| Thread Size | Thread Pitch P (mm) | Undercut Width a (mm) | Run-out length R (mm) | Undercut Diameter d₁ (mm) | |-------------|----------------------|------------------------|------------------------|-----------------------------| | M3 | 0.5 | 0.8 | 1.2 | 2.2 | | M4 | 0.7 | 1.0 | 1.6 | 3.0 | | M5 | 0.8 | 1.2 | 1.8 | 3.9 | | M6 | 1.0 | 1.5 | 2.2 | 4.7 | | M8 | 1.25 | 1.8 | 2.7 | 6.4 | | M10 | 1.5 | 2.2 | 3.2 | 8.2 |