TS ISO 5408

TS ISO 5408 is a terminology standard for screw threads, bringing together the basic terms and definitions used to describe this core mechanical feature. Screw threads are helical forms used in fastening, motion transmission and adjustment, so a common vocabulary is important for clear communication in design, manufacture and inspection.

What the thread vocabulary covers

According to the scope, the standard applies to basic terms in English and French and covers symmetrical and asymmetrical threads as well as cylindrical and tapered threads. It also states that when more than one term appears in a definition, the bold term takes priority. In practice, this helps standardise how technical definitions are read and interpreted.

From a general engineering perspective, thread geometry is more than a naming issue: pitch, profile, diameter, hand and form all affect fit, load capacity, sealing behaviour and the way parts assemble. Distinguishing cylindrical from tapered threads is especially important because these forms serve different functional purposes, while symmetrical and asymmetrical profiles are used for different load directions and operating demands. The standard supports consistent use of these concepts across technical documents and component descriptions.

The standard also notes additional terms used in definitions in Annex A, and gives equivalent terms in German, Chinese, Japanese and Swedish in Annex B for information only. The ISO terms are the English and French terms used in the standard itself.

• Defines the basic vocabulary and definitions for screw threads.
• Applies to symmetrical, asymmetrical, cylindrical and tapered threads.
• States how to prioritise terms when a definition contains more than one term.
• Provides extra terms in Annex A and informational language equivalents in Annex B.