(Transition Length): The total length including the angled chamfer leading back to the full thread.
The standard is commonly referred to in technical drawings using the notation (external threads) and DIN 76-C (internal threads), which is why many engineers search for "DIN 76A PDF."
| Feature | ISO 3508 / ISO 4755 | DIN 76-1 | | --- | --- | --- | | External thread undercut length | One type only: | Form A: 3.5P (normal) Form B: 2.5P (short) | | Internal thread specifications | Not covered | Fully specified (Form C) |
: Specifies Standard thread undercuts for external (male) threads.
Type A (normal design) with g₂ max = 3.5 P (where P is the thread pitch). din 76a pdf
) transitioning from the groove diameter back up to the thread blank diameter. Reference Dimensions for DIN 76A (Standard Undercuts)
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International distributors that offer English translations of German standards.
The standard specifies the dimensions for thread run-outs (where the thread dies out) and thread undercuts (a small groove designed to allow a thread cutting tool to exit) for both external and internal ISO metric threads (DIN 13-1). DIN 76 Type A (Normal Design) (Transition Length): The total length including the angled
(Undercut Diameter): The minor diameter of the groove. It is always smaller than the minor diameter of the thread to ensure clearance. (Undercut Width): The total axial width of the groove.
If you need the official, fully detailed engineering blueprint and tolerance charts, you will need access to the complete DIN 76-1 PDF. Official Standards Portals
If a matching female component is screwed onto this bolt, it will jam on the run-out threads before the bolt head or shoulder can firmly contact the mating surface. This creates an unsecure joint.
This public link is valid for 7 days and shares a thread, including any personal information you added. This link or copies made by others cannot be deleted. If you share with third parties, their policies apply. Can’t copy the link right now. Try again later. ) transitioning from the groove diameter back up
When a bolt or threaded shaft is machined, the thread-cutting tool cannot run cleanly directly up to a shoulder or a flat surface. This leaves an incomplete thread section known as a run-out. An undercut (or thread groove) solves this problem by:
In mechanical engineering and precision manufacturing, the integrity of a threaded joint depends heavily on how components fit together. One critical, often overlooked aspect of thread design is the thread undercut. When working with metric fasteners, the standard is the regulatory benchmark for these geometries.
When a bolt is threaded, the tool cannot cut a perfect thread all the way to a shoulder or head. DIN 76 Form A defines the specific "relief" or "undercut" area required to allow a mating part (like a nut or a plate) to sit flush against the shoulder without being blocked by the incomplete threads at the end of the shank. Key Technical Specifications
Because DIN standards are copyrighted, the most reliable and legal way to obtain an official copy is through recognized standards organizations:
Undercut DIN 76-1 – M12 – Form B → Metric thread M12 with undercut per DIN 76-1, type B.
) slightly lowers the tensile strength of the bolt at that specific cross-section.
