ISO 1122-2:1999

Overview

ISO 1122-2:1999 - "Vocabulary of gear terms - Part 2: Definitions related to worm gear geometry" is an international standard that provides precise, geometry-focused terminology for worm gears. Published as the first edition on 1999-08-01 and prepared by ISO/TC 60 (Gears), SC 1 (Nomenclature and wormgearing), this part of the ISO 1122 vocabulary standardizes terms and geometric definitions so engineers and practitioners across countries can communicate without ambiguity.

Key topics

This part concentrates exclusively on geometrical definitions related to worm gears. Key technical topics and terms covered include:

• Toroid (tore) and related toroidal elements: generant, mid-plane, mid-circle, inner circle - used to describe enveloping worm geometry.
• Worm gear pair types: definitions of cylindrical (single) worms, wormwheels, single- and double-enveloping worms and wormgear pairs.
• Reference elements for cylindrical worms: thread, reference cylinder, reference diameter, reference helix, and worm facewidth (length of the threaded part measured on the reference cylinder).
• Clarification that definitions are geometrical and intentionally rigorous to remove ambiguity in international use (figures accompany terms in the standard).

Note: The document focuses on ordinary gears with constant ratio and deliberately excludes purely theoretical or historical constructs (for example, elliptical gears or kinematic hyperboloids are not considered).

Applications

ISO 1122-2 is practical for tasks that require consistent, unambiguous language around worm gear geometry, such as:

• Gear design and specification - ensuring design intent and dimensions are communicated clearly.
• Manufacturing and gear cutting documentation - aligning machine setup, toolpaths, and production drawings.
• Quality control and inspection - defining what measurements and reference surfaces mean.
• Technical documentation, training materials, and multilingual translations - providing authoritative definitions for manuals and educational content.
• Standards development and contract specifications - reducing disputes from inconsistent terminology.

Who should use it

• Mechanical and gear designers
• Gear manufacturers and toolmakers
• Quality engineers and metrology specialists
• Technical authors, translators and educators working with gear technology
• Standards committees and procurement/specification writers

Related standards

• ISO 1122-1 - Vocabulary of gear terms: Part 1 (Definitions related to geometry) - complements Part 2 by covering broader gear geometry terminology.

Using ISO 1122-2:1999 helps organizations and professionals maintain consistent gear terminology, improve cross-border collaboration, and reduce errors in design, production, and documentation of worm gear systems.