Overview
ISO 8738:1986 specifies the requirements for plain washers for clevis pins, classified as Product Grade A. This international standard applies to plain washers manufactured in accordance with ISO 2340 and ISO 2341, covering nominal sizes from 3 mm up to and including 100 mm. The standard defines critical characteristics such as dimensions, tolerances, material properties, and surface finishes to ensure compatibility and performance in mechanical assemblies involving clevis pins.
Developed by ISO Technical Committee 2, responsible for fasteners, ISO 8738:1986 provides consistent specifications for washers used on the side of clevis pin holes. This standard promotes interchangeability, reliability, and quality in fastening systems involving articulation pins.
Key Topics
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Scope and Application
Plain washers under this standard are intended specifically for use with clevis pins, either headed or unheaded (per ISO 2340 and ISO 2341). They are to be positioned on the hole side of the pins to effectively distribute load and prevent damage or loosening.
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Dimensions and Tolerances
Detailed specifications include:
- Washer hole diameter to match nominal clevis pin diameters from 3 mm to 100 mm
- External diameters and thickness dimensions with specified minimum and maximum limits
- Surface roughness requirements for optimal fit and function
- Compliance with ISO 4759-3 for product tolerances (Classes A and C)
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Material and Hardness
The standard mandates carbon steel with a hardness range of 160 to 250 HV (Hardness Vickers), ensuring durability and wear resistance. Alternative materials can be agreed upon between client and supplier.
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Surface Finish and Coating
Preferred finishes include:
- Black oxide
- Phosphating layers
- Electroplated zinc coatings with chromate conversion (per ISO 2081 and ISO 4520)
These coatings enhance corrosion resistance and service life under various environmental conditions.
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Quality and Inspection
Washers must be free from burrs, irregularities, or any defects detrimental to mechanical performance. Inspection and acceptance follow the procedures outlined in ISO 3269.
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Designation Example
A plain washer of nominal diameter 8 mm and hardness 160 HV is designated as:
Rondelle [ISO 8738](/search?q=ISO%208738) - 8 - 16OHV
Applications
Plain washers for clevis pins under ISO 8738:1986 are widely used in:
- Mechanical linkages and joints where clevis pins enable articulation or rotation
- Automotive and aerospace assemblies requiring precise fastening and load distribution
- Heavy machinery and industrial equipment for reliable pin retention and wear protection
- Construction and agricultural machinery utilizing clevis pins in link arms and attachments
Their standardized dimensions and materials ensure compatibility with corresponding clevis pins, improving assembly efficiency and reducing maintenance downtime.
Related Standards
- ISO 2340 – Clevis pins without heads: Defines dimensions and characteristics of unheaded clevis pins compatible with these washers.
- ISO 2341 – Clevis pins with heads: Covers headed clevis pins designed to work with Grade A washers.
- ISO 4759-3 – Fastener tolerances: Specifies tolerances for washers, bolts, nuts in product Grades A and C.
- ISO 2081 – Zinc electroplated coatings on steel: Relevant for protective zinc layers on washers.
- ISO 4520 – Chromate conversion coatings: Governs chromate treatments over zinc coatings for corrosion resistance.
- ISO 3269 – Fastener acceptance inspection: Standardizes quality control procedures for washers and other fasteners.
Summary
ISO 8738:1986 provides a comprehensive framework for manufacturing and utilizing plain washers for clevis pins with assured quality, precise dimensions, and appropriate surface protection. This standard is essential for engineers, manufacturers, and quality inspectors engaged in assembling mechanical systems with clevis pins, ensuring longevity, safety, and interchangeability in industrial applications.