Overview
ISO 7091:2000 specifies the characteristics of normal-series, product-grade C plain washers manufactured in the 100 HV hardness class. The standard covers nominal sizes from 1.6 mm to 64 mm and defines suitability with specific fastener types, surface finishes and quality controls. It is intended to ensure interchangeability, consistent clamping performance and compliance with accepted inspection and testing procedures.
Key benefits: consistent dimensions, defined hardness class (100 HV), and clear guidance on acceptability and surface treatment options.
Key Topics
- Scope and suitability: Washers in this standard are suitable for hexagon bolts and screws of product grade C in property classes up to and including 6.8, for hexagon nuts of product grade C up to and including 6, and for case‑hardened thread rolling screws.
- Hardness class: The standard specifies a nominal hardness class of 100 HV and references ISO 6507‑1 for Vickers hardness testing procedures.
- Sizes and dimensions: Nominal thread diameters covered range from 1.6 mm to 64 mm. The publication includes preferred and non‑preferred dimension tables and a figure illustrating washer geometry.
- Tolerances and form: Tolerances for product grade C washers are applied in accordance with ISO 4759‑3. All tolerances apply prior to plating or coating.
- Surface finish and coatings: Plain (natural) finish washers may be supplied with a protective lubricant or coatings as agreed between customer and supplier; electroplating requirements follow ISO 4042. Non‑electrolytically applied zinc flake coatings are referenced to ISO 10683.
- Workmanship and acceptability: Parts must be free from detrimental defects and burrs. Acceptance inspection procedures are covered by ISO 3269.
- Designation example: Washer ISO 7091-8-100 HV (normal-series, product-grade C, nominal size 8 mm, 100 HV).
Applications
ISO 7091:2000 plain washers are used where standardised, reliable bearing surfaces are required between fasteners and assembled parts. Typical applications include:
- General mechanical assembly and manufacturing
- Fastening systems using grade C bolts, nuts and thread-rolling screws
- Environments requiring consistent clamping force and hardness control
Practical considerations: when clamping soft materials or where large clearance holes exist, users should verify technical suitability for the application.
Related Standards
- ISO 887 - Plain washers for metric bolts, screws and nuts (general plan)
- ISO 4759-3 - Tolerances for plain washers (product grades A and C)
- ISO 3269 - Fasteners acceptance inspection
- ISO 4042 - Electroplated coatings for fasteners
- ISO 6507-1 - Vickers hardness test method
- ISO 10683 - Non-electrolytically applied zinc flake coatings
This summary highlights the practical value of ISO 7091:2000 for procurement, design and quality control professionals who specify or supply plain washers in mechanical assemblies.