25 March 2013: Gunter Effenberger

This article presents the general standard ISO 14405-1 describing and defining tolerances of linear sizes. We do not intend to discuss every single aspect of this standard but try to focus on the contents the author considers relevant for the purpose of defining specifications, especially of creating drawings and interpreting them.

The status of ISO 14405-1 in the GPS concept

ISO 14405-1 is right below the ISO 8015 basic standard in the GPS hierarchy and represents the main standard for geometric dimensioning and tolerancing. It establishes the default specification operator – thus the default drawing indication – for linear size and provides options to modify this default specification operator.

The given definitions of sizes specified in this standard apply to all the other standards relating to this topic.

Linear sizes as a (linear) feature of size

Although the title of ISO 14405-1 refers to linear sizes, the standard itself (its contents) talks about features of size. This wording reflects the terminology of geometric tolerancing of form and location. This specialist field introduced geometrical features a long time ago.

The size of a feature of size describes its dimension as the minimum distance between opposite points of the zero-deviation, theoretical geometric form. Features of size thus do not include distances between parallel but not exactly opposite lines or planes (“step heights”), distances between two axes or midplanes or between an axis / midplane and a surface and arc lengths. These are the kind of dimensions ISO 14405-2 deals with. The ISO standard is called “Dimensional tolerancing – Dimensions other than linear sizes” but actually it could be referred to as “Other dimensions than features of size”...