Overview
ISO 724:2023 - ISO general purpose metric screw threads - Basic dimensions defines the basic dimensions for ISO general purpose metric screw threads used for fastening. This third edition (2023) updates and replaces the 1993 edition and aligns the dimensional values with the design profiles of ISO 68‑1 and the general plan of ISO 261. The standard is applicable to metric fastening screw threads and supplies the numerical basis designers, manufacturers and inspectors use to ensure thread interchangeability.
Key topics
- Scope and applicability: Basic (theoretical) dimensions for ISO metric fastening threads referenced to ISO 261 and ISO 68‑1.
- Symbols and terminology: Standardized symbols (e.g. D, d, D2, d2, P, H, H1, h3) are defined in Clause 4 and aligned with ISO vocabulary (ISO 5408).
- Dimensional formulae: Clause 5 provides formulae relating nominal major diameters, pitch (P), fundamental triangle height (H) and thread heights. Coefficients used in the standard include 0.649519·P, 1.082532·P and 1.226869·P for calculation of pitch and minor diameters; values are rounded to three decimal places.
- Comprehensive table: Table 1 lists basic dimensions (major diameter, pitch diameter, minor diameter) for a wide range of nominal diameters and standard pitches, including distinctions for internal flat crests and external rounded roots.
- Design profile reference: All values refer explicitly to the design profiles defined in ISO 68‑1.
Applications
- Mechanical design and engineering: specifying thread geometry in drawings and CAD models to ensure functional interchangeability.
- Fastener manufacturing: setting up tooling, cutting/rolling dies and machining programs based on the basic thread dimensions.
- Quality control and inspection: deriving thread gauges, pitch-diameter measurements and pass/fail criteria from standard basic dimensions.
- Procurement and standards compliance: specifying ISO‑compliant metric threads in purchase specifications for bolts, nuts and threaded components.
- Technical documentation and training: authoritative reference for educating staff on metric thread fundamentals.
Who uses ISO 724:2023
- Mechanical engineers and product designers
- Fastener manufacturers and toolmakers
- Metrology and quality assurance personnel
- CAD/CAE modelers and CAM programmers
- Standards committees and technical libraries
Related standards
- ISO 261 - ISO general purpose metric screw threads - General plan
- ISO 68‑1 - Basic and design profiles for metric screw threads
- ISO 5408 - Screw threads - Vocabulary
Keywords: ISO 724:2023, metric screw threads, basic dimensions, pitch diameter, minor diameter, ISO general purpose, ISO 261, ISO 68-1, fastening threads, thread standards.
