Gewindegrund

Gewindegrund is a term used in mechanical engineering to refer to the root or core diameter of a screw thread. It denotes the smallest diameter formed by the thread profile along the axis of the fastener or threaded hole. In practice, the Gewindegrund is the limiting diameter that determines how much material is engaged in the threaded connection and thus influences strength, load capacity, and fit.

In standard thread geometry, the major diameter describes the largest extent of the external thread, while the pitch diameter is a midline reference used for tolerance calculations. The Gewindegrund (core or minor diameter) sits at the opposite end of the spectrum and corresponds to the diameter at the bottom of the thread valleys. The difference between the major diameter and the Gewindegrund gives the thread depth, a value determined by the thread form (for example metric or imperial standards) and its tolerances.

The Gewindegrund is defined by applicable DIN/ISO thread standards and tolerance classes. When designing or producing threaded parts, engineers use the Gewindegrund to select appropriate tapping or drilling sizes for internal threads and to ensure adequate engagement with mating parts. Accurate specification of the Gewindegrund is essential for predicting joint strength, leakage potential, and service life, especially in high-load or precision applications.

Note that terminology can vary by industry; Gewindegrund is often discussed alongside Kern-Durchmesser (core diameter) and Gewindekernmaß, with the latter terms used in different texts to describe the same concept.