(Transition Radius) : The smooth curve linking the groove to the shoulder, vital for minimizing stress concentration. Standard Dimensions Reference Table

If a nut or threaded component is screwed onto a shaft that lacks a proper run-out, the nut will bottom out on an incomplete thread, preventing a secure clamp load. DIN 76-A ensures that the nut can seat fully against the shoulder.

The standard is a cornerstone of precise mechanical design, ensuring that external metric threads can be manufactured efficiently and assembled without mechanical interference. By understanding how the thread pitch dictates the undercut width, diameter, and radius, engineers can create robust designs that mitigate stress concentrations and facilitate smooth manufacturing workflows.

DIN 76 is the industry-standard blueprint for ensuring that threaded fasteners actually fit together. Specifically, 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

The transition area where the thread depth gradually decreases to zero.

: Fasteners with thread undercuts may have reduced load-bearing capacity compared to those with standard run-outs. Din 76-1 | PDF | Screw | Metalworking - Scribd

It is designed to work seamlessly with DIN 13-1 , which defines the core ISO metric thread dimensions. Practical Resources

However, it is crucial to stress that the precise, legally valid dimensional data for Form A and Form B is exclusively contained within the official, copyrighted . While third-party websites may host scanned copies, these are generally unauthorized distributions and often subject to copyright infringement [14†L4-L8].

A DIN 76 Form A undercut solves this by removing a small section of metal right before the shoulder. This provides several critical engineering benefits: