Overview
ISO 17:1973, titled Guide to the use of preferred numbers and of series of preferred numbers, is an international standard published by the International Organization for Standardization (ISO). The document provides comprehensive guidance on selecting and utilizing preferred numbers-standardized numerical values arranged in geometrical progressions. These preferred numerical series are designed to create rational and efficient grading systems in manufacturing, engineering, and design. By adopting these series, industries can reduce material waste, optimize tooling costs, and minimize stock inventory values.
The standard addresses the balance between using scales with too-wide steps-which increase waste and manufacturing costs-and scales with too-narrow steps-which drive up tooling and inventory expenses. The ISO 17 framework promotes the selection of series with the highest ratio suitable for specific requirements, typically prioritizing R5, then R10, and so forth.
Key Topics
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Preferred Numbers Concept
Preferred numbers are rounded values derived from specific geometrical progressions. Initially developed by Captain Charles Renard in the late 19th century, these numbers allow standardized gradations used universally in various technical fields.
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Series of Preferred Numbers
The main series covered include R5, R10, R20, and R40, where each subsequent series has a ratio often equal to the square root of the previous series' ratio. These series provide consistent, scalable steps suited for standardized measurements.
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Geometrical Progressions and Rounding
The standard details the mathematical properties of these preferred numbers as terms in geometric progressions with ratios that are roots of 10. It also explains how rounding deviations of approximately +1.26% to -1.01% are permissible and affect calculations.
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Application Guidelines
Practical recommendations encourage the use of the broadest ratio series (such as R5 before R10) to minimize complexity, while ensuring the selected series fits the desired balance of cost-efficiency and precision. Variations like derived and shifted series allow flexibility for different industrial requirements.
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Calculation Methods
ISO 17 provides methods to compute products, quotients, powers, and roots involving preferred numbers, utilizing serial numbers and logarithmic relationships to maintain precision within acceptable tolerances.
Applications
ISO 17:1973 is highly practical for sectors where standardized numerical gradations are critical, including:
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Manufacturing and Production Engineering
Optimizing product dimensions and sizes to reduce tooling costs and material waste.
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Design and Quality Control
Establishing consistent specifications across product lines and industries.
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Inventory and Supply Chain Management
Minimizing stock variations and simplifying procurement with standardized part sizes.
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Electrical and Mechanical Engineering
Standardizing parameters, such as motor speeds and component dimensions, for improved interoperability and maintenance.
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Construction and Infrastructure
Applying rational grading systems for components and materials to optimize project costs and efficiency.
Related Standards
ISO 17 is closely linked with the following standards that further elaborate on preferred numbers and their applications:
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ISO 3 - Preferred numbers - Series of preferred numbers
Provides detailed tables of preferred numbers and their practical rounding.
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ISO 497 - Guide to the choice of series of preferred numbers and of series containing more rounded values of preferred numbers
Offers guidance on the use of more rounded preferred numbers when standard preferred numbers are impractical.
These related documents complement ISO 17 and provide additional frameworks for selecting appropriate numerical series tailored to specific industrial needs.
By integrating ISO 17:1973 into product development and manufacturing processes, organizations ensure standardized, cost-efficient grading of numerical values that adhere to internationally recognized best practices. This enhances operational efficiency, reduces unnecessary costs, and promotes consistency across global markets.