Overview
ISO 5408:2009 - Screw threads - Vocabulary is an international standard that specifies the fundamental terms and definitions used for screw threads. The vocabulary covers both symmetrical and unsymmetrical threads, and both cylindrical (parallel) and taper (conical) threads. The document is published in English and French (the two official ISO terms), with informative equivalents in German, Chinese, Japanese and Swedish given in annexes. This second edition replaces ISO 5408:1983 and was prepared by ISO/TC 1 (Screw threads).
Key topics and requirements
ISO 5408:2009 standardizes the language and core concepts used across design, manufacturing and inspection of threaded components. Key technical topics include:
- Helix, lead and lead angle - definitions of the helical curve, axial lead (pitch for metric single-start), and the helix angle on cylinders and cones.
- Types of screw threads - definitions for cylindrical (parallel) threads, taper (conical) threads, symmetrical and unsymmetrical threads.
- Thread orientation and starts - single-start vs multistart, right-hand and left-hand threads.
- External and internal threads - distinctions between bolt (external) and nut (internal) threads.
- Profile terminology - fundamental triangle, basic profile, crest/root truncation and related geometric terms used in thread profiles.
- Defect and feature terms - thread runout (washout), thread start and other finish-related definitions.
- Normative reference: ISO 286-1:1988 (ISO system of limits and fits - bases of tolerances, deviations and fits) is cited as indispensable for application.
Notes and illustrations (figures) accompany many definitions to clarify geometric relationships. The standard also states reproduction conditions for the included terms and definitions (educational/implementation use with citation).
Applications
ISO 5408:2009 is used to ensure consistent terminology across:
- Technical drawings, specifications and part catalogs
- Design and engineering documentation for fasteners and threaded components
- Manufacturing process documentation (cutting, rolling, tapping)
- Quality control, inspection reports and metrology procedures
- Teaching materials, training and standards-based instruction
- International procurement and contracts where unambiguous thread terminology is critical
Who should use this standard
- Mechanical design and R&D engineers
- Manufacturing engineers and machinists
- Quality and metrology professionals
- Technical writers, standards committees and educators
- Purchasing and specification authors sourcing threaded components internationally
Related standards
- ISO 286-1:1988 (limits and fits) - normative reference in ISO 5408:2009
- Prepared by ISO/TC 1 - Screw threads; consult ISO for other thread profile or fastener standards when combining vocabulary with dimensional and tolerance rules.
Keywords: ISO 5408:2009, screw threads, thread vocabulary, helix, lead, pitch, thread profiles, cylindrical threads, taper threads, thread terminology.
