ISO 8678:1988

Overview

ISO 8678:1988 covers cup head square neck bolts with small head and short neck, defined as product grade B. The standard specifies metric thread sizes from M6 up to and including M20 and tabulates nominal lengths from 12 mm to 160 mm. It establishes dimensional definitions, tolerance classes and references to related ISO documents to ensure interchangeability, reliable mechanical performance and consistent selection of fasteners.

Key Topics

• Scope: Metric dimensions and threads M6–M20; nominal lengths 12–160 mm. Product grade B fasteners.
• Dimensions & designation: Standard tabulates thread sizes and nominal/maximum/minimum dimensions. Example designation given in the standard: Cup head Square neck bolt ISO 8678 - M12 x 80 - 8.8.
• Thread and tolerance: Threads referenced to ISO 261 and ISO 965-2; common tolerance class indicated in the standard is 6g.
• Mechanical properties: Recommended property classes include 4.8, 8.8 and 10.9, with mechanical requirements referenced to ISO 898-1.
• Acceptability and surface conditions: Acceptance inspection and surface-discontinuity limits are covered by ISO 3269 and ISO 6157 series.
• Finishes and coatings: Electroplating requirements are referenced in ISO 4642; hot-dip galvanizing in ISO 1461. Specific finishes should be agreed between supplier and customer.

Applications

ISO 8678:1988 is targeted at engineers, purchasers and fastener manufacturers who need a standardized specification for cup head square neck bolts when:

• Designing assemblies that require positive anti-rotation provided by the square neck beneath the head.
• Selecting metric fasteners for machinery, structural fittings or equipment where compact head form and short neck are required.
• Ensuring interchangeability across suppliers by referencing a recognized ISO product grade.

Benefits of using ISO 8678:1988 include predictable dimensions for design integration, clear guidance on thread/tolerance coordination, and simplified procurement through an accepted designation format.

Related Standards

ISO 8678 cross-references several international standards for complementary requirements and tolerances:

• ISO 225 (dimension symbols and designations)
• ISO 261, ISO 965-2 (metric threads and tolerances)
• ISO 888 (nominal/thread lengths)
• ISO 898-1 (mechanical properties of fasteners)
• ISO 4759-1 (tolerances for fasteners: grades A, B, C)
• ISO 4642 (electroplated coatings)
• ISO 1461 (hot-dip galvanizing)
• ISO 3269 (acceptance inspection)
• ISO 6157-1 / ISO 6157-3 (surface discontinuities)

Use ISO 8678:1988 as the dimensional and designation baseline for cup head square neck bolts (small head, short neck) and consult the referenced standards for material, coating, inspection and detailed thread/tolerance requirements.