) 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:
According to the DIN 76-1 PDF , Form A represents the for external thread undercuts. It is the default choice for engineering drawings unless technical constraints (such as space limitations) require the shorter Form B. Specification for Form A (Normal) Application External ISO metric threads (coarse or fine). Undercut Width ( ) Typically calculated as (where is the thread pitch). Undercut Diameter ( )
Form A is typically preferred; Form B is a "short" version used only in special cases where space is limited. BAER Tools Accessing the PDF din 76-a pdf
: It allows the mating female component to screw completely down to the shoulder without interference.
: Used for external threads with short undercut depths (often for compact spaces). ) on every single threaded shoulder—which clutters the
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:
If your drawing is specifically detailing metric fine threads or requires specific tolerances, you may include the thread size alongside it: It is the default choice for engineering drawings
Note: $d$ is the major diameter of the thread.
The standard is divided into several parts based on the type of thread being used:
Most reputable mechanical engineering handbooks reproduce the DIN 76-A tables legally in their fasteners and threading sections.
| Thread size (M) | Pitch P (mm) | Undercut width a (mm) | Undercut depth t (mm) | |----------------|--------------|------------------------|------------------------| | M3 | 0.5 | 0.8 | 0.15 | | M4 | 0.7 | 1.0 | 0.20 | | M5 | 0.8 | 1.2 | 0.25 | | M6 | 1.0 | 1.5 | 0.30 | | M8 | 1.25 | 1.8 | 0.35 | | M10 | 1.5 | 2.0 | 0.40 | | M12 | 1.75 | 2.5 | 0.50 | | M16 | 2.0 | 3.0 | 0.60 |