Din 76-a Pdf

Note: For exact values, always refer to the official tables in the DIN 76-A PDF, as values vary by thread size (M3 to M100+).

: The undercut diameter is always smaller than the minor diameter of the thread. Width : Typically about 3 times the thread pitch ( Angles : Standard transition angles are either 30° or 60° . din 76-a pdf

: Provides a breakdown of run-outs and undercuts for metric threads. Note: For exact values, always refer to the

is the German standard that specifies the dimensions for thread run-outs and thread undercuts specifically for ISO metric threads (coarse and fine pitch). : Provides a breakdown of run-outs and undercuts

| Thread Pitch ($P$) | Width of Undercut ($a$) | Radius ($r_1$) | Undercut Diameter ($d_3$) | | :--- | :--- | :--- | :--- | | 1.0 mm | 2.0 mm | 0.5 mm | $d - 1.6$ | | 1.25 mm | 2.5 mm | 0.6 mm | $d - 2.0$ | | 1.5 mm | 3.0 mm | 0.8 mm | $d - 2.4$ | | 1.75 mm | 3.5 mm | 1.0 mm | $d - 2.8$ | | 2.0 mm | 4.0 mm | 1.0 mm | $d - 3.2$ | | 2.5 mm | 5.0 mm | 1.2 mm | $d - 4.0$ |

When a threaded section transitions abruptly to a plain shaft (a sharp corner), it creates a tremendous stress concentration. Under cyclic loads or vibration, this sharp corner becomes a failure point, leading to cracks and eventual fracture. The undercut defined in DIN 76-A rounds this corner, distributing stress evenly.