ISO 2903-2:2025

Overview

ISO 2903-2:2025 - "ISO metric trapezoidal screw threads - Tolerances - Part 2: Limits of sizes" (first edition, July 2025) specifies the permissible limits of sizes for major, pitch and minor diameters of ISO metric trapezoidal screw threads (Tr). It applies to threads conforming to ISO 2902 with basic/design profiles per ISO 2901, and covers the seven tolerance classes recommended in the ISO 2903 series: 7H, 8H, 9H, 7e, 8e, 8c and 9c.

Key topics and technical requirements

• Scope: limits of sizes for major, pitch and minor diameters of internal and external trapezoidal threads.
• Basis: limits are derived from the fundamental deviations and tolerances in ISO 2903 and are calculated by specified formulae, then rounded to the third decimal place.
• Content structure:
  • General formulae and symbol definitions (referenced to ISO 2903).
  • Detailed tables of limits of sizes for internal and external threads across nominal diameters (tables cover nominal ranges up to 300 mm for certain classes).
  • Notes such as the maximum major diameter of internal thread not being specified and that some parameters (e.g., es) can be negative.
• Normative references: ISO 2903 (series) and ISO 5408 (screw thread vocabulary).
• Practical deliverables: standard tables (e.g., Table 1–Table 8) listing limits for each tolerance class and nominal diameter.

Applications and who uses it

ISO 2903-2:2025 is intended for professionals who design, manufacture, inspect or procure trapezoidal screw threads used in:

• Mechanical and machine-tool designers specifying lead screws, jacks, linear actuators, vises and power-transmission screws.
• Manufacturing engineers and CNC programmers setting machining allowances and thread-cutting parameters.
• Quality engineers, metrologists and inspection labs verifying thread dimensions and ensuring interchangeability.
• Component and fastener suppliers, purchasers and standards committees verifying compliance with international tolerance systems.

Practical benefits include consistent dimensioning for mating parts, clear acceptance criteria for inspections, and reduced risk of assembly/interchangeability problems.

Related standards

• ISO 2901 - basic and design profiles for metric trapezoidal screw threads
• ISO 2902 - general requirements for ISO metric trapezoidal screw threads
• ISO 2903 - tolerances (series overview and fundamentals)
• ISO 5408 - screw threads - vocabulary

Keywords: ISO 2903-2:2025, ISO metric trapezoidal screw threads, thread tolerances, limits of sizes, tolerance classes 7H 8H 9H 7e 8e 8c 9c, major pitch minor diameter.