ISO 48-4:2018

Overview

ISO 48-4:2018 specifies the standardized method for determining the indentation hardness (Shore hardness) of vulcanized or thermoplastic rubber using a durometer. The document defines the A, D, AO and AM durometer scales, the required apparatus, test-piece preparation, conditioning, measurement procedure, calibration/verification and reporting requirements. ISO 48-4:2018 replaces ISO 7619-1:2010 and is part of the grouped ISO 48 series on rubber hardness.

Keywords: ISO 48-4:2018, Shore hardness, durometer, indentation hardness, rubber testing, vulcanized rubber, thermoplastic rubber.

Key topics and technical requirements

• Scope and scales: Covers the A scale (normal hardness), D scale (high hardness), AO scale (low-hardness and cellular rubbers) and AM scale (thin test pieces).
• Choice of scale: Guidance on selecting scale (e.g., use AM for test pieces < 6 mm; switch between A and D or AO for low/high readings).
• Apparatus:
  • Pressure foot dimensions (types A/D: 18 mm ± 0.5 mm diameter with a central hole; AO: minimum area and specified central hole dimensions for stand use).
  • Indentor geometry (hardened-steel rod, diameter ~1.25 mm ± 0.15 mm for A/D; AO radius 2.5 mm ± 0.02 mm).
  • Indicating device calibrated from 0 (maximum protrusion) to 100 (zero protrusion).
  • Calibrated spring requirements with force-to-reading relationships (e.g., F = 550 + 75·H for type A; F = 445·H for type D).
  • Optional automatic timing device and a stand for improved precision.
• Procedure elements: Test-piece preparation, conditioning and specified test time before reading; measurement technique and number of readings; calibration and verification using reference blocks.
• Quality and precision: Calibration, periodic checking, and precision data (informative annex) to support reproducible results.
• Reporting: Required information for test reports to ensure traceability and comparability.

Applications and users

ISO 48-4:2018 is intended for:

• Quality control and acceptance testing in rubber manufacturing (vulcanized and thermoplastic products).
• Product development and material characterization for seals, hoses, gaskets, tires, footwear and other rubber components.
• Test laboratories performing standardized hardness measurements for suppliers, OEMs and regulatory compliance.
• Engineers and procurement specialists who require comparable Shore hardness values for specification and selection of rubber materials.

Practical benefits include consistent hardness measurement across labs, improved precision using stands and calibration routines, and clear guidance on scale selection for different rubber types and thicknesses.

Related standards

• ISO 48 series (other parts covering related hardness methods)
• ISO 48-9 - Calibration and verification of hardness testers
• ISO 23529 - Preparation and conditioning of rubber test pieces

For consistent results, users should follow ISO 48-4:2018 together with the relevant calibration and test-piece preparation standards.