December 2025: New Gear and Bearing Standards Enhance Mechanical Systems

In December 2025, the mechanical systems sector saw the publication of two pivotal international standards designed to advance precision, reliability, and safety. Professionals working with gears and bearings will welcome the arrival of ISO 21771-2:2025 and ISO 7148-1:2025, both of which bring updated methodologies, definitions, and guidance to ensure higher quality and performance in diverse applications. These standards set the benchmark for design verification and testing in mechanical components, influencing manufacturing, inspection, and product lifecycle management. This article provides a comprehensive analysis of each newly published standard, detailing their implications, principal requirements, and implementation recommendations.

Overview of the Mechanical Systems Sector and the Role of Standards

Mechanical systems and components for general use form the backbone of virtually every industrial domain—ranging from automotive and aerospace to manufacturing, robotics, and heavy equipment. Central elements such as gears and plain bearings are critical to mechanical performance, operational efficiency, and safety.

International standards in this field ensure that these core components are designed, manufactured, and tested to strict, globally recognized criteria. This harmonization facilitates:

• Interchangeability of parts
• Reliability in operation under diverse conditions
• Safety and performance across all stages of product development
• Effective compliance with regulatory and customer requirements

Professionals reading this article will learn about the technical scope, new or revised requirements, and operational impacts of the latest standards. Direct links to each ISO publication are provided for in-depth exploration and adoption.

Detailed Standards Coverage

ISO 21771-2:2025 – Calculation and Measurement of Gear Tooth Thickness and Backlash

Cylindrical involute gears and gear pairs — Part 2: Calculation and measurement of tooth thickness and backlash

Published by ISO in December 2025, ISO 21771-2:2025 is a comprehensive resource for anyone involved in the design, manufacturing, inspection, or maintenance of cylindrical involute gears and gear pairs. This standard supersedes earlier guidance provided by ISO/TR-10064-1 and ISO 21771-1, amalgamating established international practices with the latest advances in gear metrology.

Scope and Application:

• Applicable to external and internal parallel axis cylindrical involute spur and helical gears, involute worms and crossed axis gears, spur and helical racks, and involute sector gears.
• Covers gears of all sizes and materials, regardless of production method.
• Focuses on calculation procedures for specification limits when desired tooth thickness is known, as well as relationships among tooth thickness, backlash, centre distance, and tooth deviations.

Key Requirements and Specifications:

• Defines precise terminology and measurement methodologies for both tooth thickness and backlash, supporting standardization in documentation and reporting.
• Provides formulae and methods (pitch measurement, double and single flank testing, span measurement, three ball/pin measurements, chordal methods, and more) to cover a wide variety of gear geometries and inspection constraints.
• Outlines datum surfaces and datum axis considerations fundamental to gear metrology.
• Presents calculations for normal and transverse tooth thickness, backlash types (circumferential, transverse, normal, axial, radial, angular), and the implications of manufacturing profile shift coefficients.
• Details the advantages, limitations, and assumptions for each measurement method, enabling selection of the most suitable technique for a given application.

Target Industries and Organizations:

• Gear and transmission manufacturers
• Automotive, aerospace, and industrial machinery producers
• Quality assurance teams and calibration labs
• Design engineers and R&D professionals

Practical Implications:

• Enhances consistency and reproducibility in gear measurement and reporting across organizations and geographies.
• Facilitates accurate determination of gear specification compliance and fit for purpose.
• Informs the effective specification of gear properties in contracts and technical drawings.

Notable Changes from Previous Editions:

• Incorporates content relevant to new gear types, such as crossed axis gears and sector gears.
• Introduces advanced methodologies for measurement using three ball span devices.
• Expands definitions, test procedures, and example calculations for faster onboarding and correct application.

Key highlights:

• Covers multiple industry-standard measurement techniques for gears
• Enriches terminology and calculation guidance for designers and inspectors
• Ensures compatibility with both legacy and advanced manufacturing processes

Access the full standard:View ISO 21771-2:2025 on iTeh Standards

ISO 7148-1:2025 – Testing the Tribological Behaviour of Bearing Metals

Plain bearings — Testing of the tribological behaviour of bearing materials — Part 1: Testing of bearing metals

The newly published ISO 7148-1:2025 offers authoritative test protocols for evaluating the friction and wear properties (tribological characteristics) of metallic bearing materials under boundary lubrication. This standard is instrumental for ensuring the long-term reliability and safety of plain bearing systems used in demanding industrial environments.

Scope and Application:

• Specifies tribological test procedures for metallic bearing materials in plain bearings.
• Focused on boundary lubrication conditions, which are prevalent during startup, shutdown, or whenever hydrodynamic lubrication cannot be sustained.
• Covers test preparation, execution, specimen characteristics, and result reporting for comparative analysis of bearing material/lubricant combinations.

Key Requirements and Specifications:

• Outlines multiple standard test methods, including:
  • Pin-on-disc (vertical/horizontal)
  • Block-on-ring
  • Rotating under thrust load (sleeve-to-sleeve, sleeve-to-plate)
• Defines the shape, preparation, and properties of test specimens (discs, pins, rings, blocks, sleeves, plates) to ensure uniformity and comparability of results.
• Specifies data collection parameters: coefficient of friction, wear rate, sliding distance, surface parameters (Ra, Rk, Rpk, Rvk), tensile strength, proof stress, compression limit, and lubricant viscosity.
• Provides structured reporting requirements, ensuring clarity in test results and traceability back to test conditions and materials used.
• Emphasizes the importance of close alignment between test conditions and real-world application for accurate material selection.

Target Industries and Organizations:

• Bearing manufacturers and suppliers
• Tribology researchers and R&D departments
• Quality and material testing laboratories
• Sectors using heavy machinery, such as energy, mining, marine, transport

Practical Implications:

• Sets standardized methodologies for material comparison and selection, enabling manufacturers to validate new bearing materials or lubricants.
• Supports quality assurance by defining universally accepted test procedures, reducing disputes and enhancing marketplace confidence.

Notable Changes from Previous Editions:

• Updated normative references and expanded definitions
• Revised and new tables for clearer method comparisons
• Enhanced specimen preparation and test reporting requirements

Key highlights:

• Covers a broad spectrum of tribological test methods for metallic bearings
• Establishes robust procedures for comparing new materials or lubricants
• Enhances material sourcing, selection, and compliance processes industry-wide

Access the full standard:View ISO 7148-1:2025 on iTeh Standards

Industry Impact & Compliance

How These Standards Affect Businesses

The adoption of ISO 21771-2:2025 and ISO 7148-1:2025 will positively impact the design, manufacture, and maintenance of mechanical systems. Key impacts include:

• Increased precision and reliability of gears and bearings in high-performance applications
• Streamlined quality assurance and supplier qualification processes—results become easier to compare, verify, and audit
• Reduced product failures and costly rework thanks to reproducible measurement and testing
• Enhanced international competitiveness by aligning with the latest globally recognized standards

Compliance Considerations and Timelines

• For OEMs and suppliers, timely transition to these updated standards is critical for tender processes and regulatory approval.
• Initiatives should include updating internal procedures, calibrating measurement/test equipment, and retraining relevant personnel.
• End-users and specifiers should demand these standards in contracts and product qualifications from 2026 onward.
• Periodic reviews and audits of compliance documentation should be scheduled to ensure ongoing conformance.

Benefits of Adopting These Standards

• Improved product integrity and safety
• Market access to clients requiring ISO-compliant products
• Reduced warranty and liability exposure due to standardized quality controls
• Technical documentation harmonized globally, simplifying supply chain collaboration

Risks of Non-Compliance

• Increased likelihood of gear or bearing failure, leading to costly operational downtime
• Risk of audit findings, non-conformance penalties, or contract loss
• Reduced competitiveness in regulated or standards-driven markets

Technical Insights

Common Technical Requirements Across the Standards

• Precision in Measurement and Testing: Both standards stress the use of calibrated, validated equipment and well-defined operating procedures.
• Consistent Documentation: Clear, unambiguous reporting formats enable data comparability and traceability.
• Terminology and Symbol Uniformity: Adhering to harmonized definitions (e.g., tooth thickness, backlash, coefficient of friction) across the industry streamlines communication.

Implementation Best Practices

1. Gap Analysis: Benchmark current procedures against new standard requirements.
2. Training: Invest in focused training for metrology, QA/QC, and R&D staff.
3. Equipment Calibration: Ensure all gear measuring tools, tribology testers, and data acquisition systems are recalibrated to standard-defined tolerances.
4. Documentation Updates: Revise technical specifications, work instructions, and supplier documents.
5. Supplier Engagement: Confirm that supply chain partners also comply with updated standards.

Testing and Certification Considerations

• Engage accredited third-party labs for initial validation of testing and measurement processes
• Document all calibration and maintenance of test and inspection equipment
• When possible, participate in round-robin or interlaboratory testing to ensure data reliability
• Maintain detailed records of compliance for future audits or regulatory reviews

Conclusion and Next Steps

The December 2025 release of ISO 21771-2:2025 and ISO 7148-1:2025 marks a significant advancement in the evolution of standards for mechanical systems and components for general use. By embracing these new specifications, organizations can dramatically increase the quality, reliability, and global acceptance of their products.

Key takeaways:

• Both standards offer robust frameworks for measurement and testing, relevant to a broad spectrum of mechanical and manufacturing industries.
• Early adoption and internal alignment will drive competitive advantage and quality outcomes.
• Continued engagement with the latest revisions through platforms like iTeh Standards will position companies at the forefront of best practices.

Recommendations:

• Review the full standards for detailed requirements and guidance.
• Update company procedures, equipment, and training to reflect the new editions.
• Engage with quality and compliance teams to integrate these standards into daily practice.

Explore these and other essential mechanical standards today on iTeh Standards.