Overview
ISO 15786:2008 - Technical drawings - Simplified representation and dimensioning of holes - defines rules for how to show, dimension and toleranced holes, counterbores, internal threads and chamfers on engineering drawings using simplified graphical and textual conventions. It specifies when simplified methods are acceptable and when complete representations (cuts, sections, enlarged views) must be used to avoid ambiguity.
Key SEO phrases: ISO 15786:2008, technical drawings, simplified representation, dimensioning of holes, counterbores, internal threads, chamfers, tolerancing.
Key topics and requirements
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Methods of representation
- Complete representation and complete dimensioning (full views, sections) when simplification could mislead.
- Complete representation with simplified dimensioning.
- Simplified representation and simplified dimensioning (only centre lines or symbolic markers).
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Structure and sequence
- Simplified dimensioning is a vertical sequence of descriptive elements arranged largest-to-smallest (symbols, nominal sizes, depths, tolerances).
- Use consistent character sizing and single-line instructions for identical features or groups.
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Graphical symbols
- Standard symbols include ∅ (diameter), square symbol, and hole‑bottom symbols U, V, W.
- Countersink/chamfer shown by largest diameter × angle; depths by the multiplication sign × and threaded/cored distinctions using a slash / (e.g., M10×25/30).
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Groups and repetition
- Indicate number of groups and holes per group with notation such as 3×/5× ∅10 or 5× ∅10; use textual descriptions only where necessary (avoid for automated data transfer).
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Tolerancing & surface finishes
- Dimensions must be toleranced (direct tolerances or general tolerances such as ISO 2768‑1).
- Surface texture and geometrical tolerances follow ISO GPS standards referenced by ISO 15786.
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Leader lines & orientation
- Leader lines terminate at hole centres or at the intersection of the centre line and visible edge; arrow direction indicates the surface from which features are manufactured.
Practical applications and users
Who benefits:
- Mechanical drafters and CAD technicians creating standardized drawings.
- Design engineers specifying holes, threads and countersinks for manufacturability.
- Manufacturing engineers and machinists interpreting production drawings.
- Quality/control engineers inspecting features to specified tolerances.
- Technical publications teams and organizations using automated drawing data exchange.
Typical uses:
- Producing concise, unambiguous manufacturing drawings for machined parts.
- Reducing drawing clutter by using simplified notation where appropriate.
- Standardizing cross-company drawing conventions for procurement and inspection.
Related standards
ISO 15786 references and complements other drawing and GPS standards, including:
Using ISO 15786:2008 helps ensure clear, consistent hole representation and dimensioning across engineering and manufacturing workflows.
