Overview
ISO 2904:2020 specifies the basic dimensions of ISO metric trapezoidal screw threads. It defines the reference sizes for design profiles (per ISO 2901) and aligns with the general planning rules of ISO 2902. The standard is the second edition (2020), updating and replacing the 1977 edition. It is chiefly applicable to traversing threads used for linear (traversing) motion on machines and tools, and it may also be used where trapezoidal threads are used for fastening.
Key topics
- Scope and applicability: Basic dimensional data for ISO metric trapezoidal threads intended primarily for motion (lead/lead-screw) and, secondarily, for fastening.
- Normative references and terminology: Uses ISO 5408 for thread vocabulary; design/profile references link to ISO 2901 and ISO 2902.
- Symbols and definitions: Standardized symbols for diameters (basic major, pitch, minor for internal and external threads), pitch (P), clearance (a), and corner radius (c).
- Calculation method: Table of basic dimensions (nominal diameter, pitch, basic pitch/major/minor diameters) is provided. Values are derived from formulae relating nominal diameter (d), pitch (P), clearances and corner radii and are rounded to the third decimal place.
- Tabulated data: Table 1 presents pre-calculated basic dimensions across a broad range of nominal diameters and standard pitches for quick reference and specification.
Applications
ISO 2904:2020 is used by professionals and organisations involved in mechanical design and manufacture where trapezoidal threads are required:
- Machine designers and mechanical engineers specifying lead screws, feed screws, jacks, actuators and positioning mechanisms.
- Manufacturers and suppliers of threaded parts, nuts and leadscrews for ensuring consistent production to international dimensional norms.
- Quality, inspection and metrology teams creating gauges, inspection plans and acceptance criteria based on basic dimensions.
- CAD/CAM libraries and technical documentation teams standardizing component models and drawing callouts.
Practical benefits include improved interchangeability, predictable fit/clearance for traversing motion, and streamlined procurement and inspection.
Related standards
- ISO 2901 - ISO metric trapezoidal screw threads - Basic and design profiles
- ISO 2902 - ISO metric trapezoidal screw threads - General plan
- ISO 5408 - Screw threads - Vocabulary
Keywords: ISO 2904:2020, trapezoidal screw threads, ISO metric trapezoidal, basic dimensions, lead screw standard, traversing threads, thread pitch, thread design.