ISO 21920-2:2021

Overview

ISO 21920-2:2021 - Geometrical product specifications (GPS) - Surface texture: Profile - Part 2 defines the terms, definitions and surface texture parameters used to determine profile-based surface texture. Published in December 2021, this first edition consolidates and updates earlier profile standards (e.g., ISO 4287, ISO 12085, ISO 13565 series) and aligns profile parameters with the ISO GPS matrix model. The document is focused on profile measurement methods and establishes a common vocabulary and parameter set for consistent specification, measurement and reporting.

Key topics and technical requirements

• Terminology and definitions for profile surface texture, including general terms, geometrical parameters and feature terms.
• Field parameters organized by type:
  • Height parameters (e.g., arithmetic mean height, root mean square height, skewness, kurtosis, total height)
  • Spatial parameters (e.g., autocorrelation length, dominant spatial wavelength)
  • Hybrid parameters (e.g., root mean square gradient, developed length and ratios)
  • Material ratio functions and related parameters, including material ratio curve and volume parameters
• Feature parameters based on peak/pit characterization and profile-element segmentation (spacing, heights, counts).
• Feature characterization methods and named feature parameters, including normative procedures for segmentation (crossing-the-line, watershed-related approaches noted as an update).
• Normative and informative annexes providing calculation methods (derivatives, curvature), determination procedures (material ratio curve, stratified surfaces), segmentation and feature-characterization workflows, and a summary of parameters.
• References to filtration and GPS concepts (ISO 16610-1, ISO 14638) and decision rules (ISO 8015, ISO 14253-1) to ensure consistent application.

Practical applications

• Specifying and verifying surface roughness and texture on engineering drawings and quality documents.
• Supporting manufacturing process control (turning, milling, grinding, honing) by defining measurable texture metrics for acceptance.
• Enabling tribology and sealing performance analysis where profile features (peaks, valleys, material ratio) affect friction, wear and lubrication.
• Guiding metrology labs and instrument manufacturers on standardized parameter definitions and calculation methods for profilometers and evaluation software.
• Useful for surface engineering, coatings, functional surfaces and failure analysis where quantitative profile descriptors are required.

Who should use this standard

• Metrology and quality engineers, inspection labs, instrument and software developers, manufacturing engineers, design engineers specifying surface requirements, and standards committees working on GPS and surface metrology.

Related standards

• ISO 21920 series (profile and areal surface texture standards)
• ISO 16610-1 (filtration concepts)
• ISO 14638 (GPS matrix model)
• ISO 8015 and ISO 14253-1 (GPS rules and decision rules)

Keywords: ISO 21920-2, surface texture, profile, GPS, surface roughness parameters, Ra, Rq, autocorrelation length, material ratio curve, surface metrology.