Overview
ISO 6411:1982 - Technical drawings - Simplified representation of centre holes defines a compact way to show centre holes on engineering drawings when the exact form and size are not required. The standard lets designers use standardized centre‑hole symbols and a concise designation (e.g., “ISO 6411‑B 2,5/8”) instead of full detailed geometry. Annex A provides preferred dimensions for types R, A and B, and Annex B gives symbol proportions and drawing‑presentation rules.
Key topics and requirements
- Scope and purpose: Use simplified representation particularly when the designation of a standardized centre hole is sufficient for manufacturing or inspection information.
- Three drawing requirements:
- Centre hole is required on the finished part.
- Centre hole may be present but is not essential.
- Centre hole shall not exist on the finished part.
- Designation format:
- Consists of a reference to the standard, the letter for the type (R, A or B) and the pilot diameter. Two values (pilot diameter d and outside countersink diameter D) are separated by a solidus. Examples in the standard: ISO 6411‑B 2,5/8 and ISO 6411 R 3,15/6,7.
- Interpretation of designations: Annex A (table 3) shows the dimensions associated with preferred sizes for types R, A and B; the designation can be referenced to ISO or other national standards for centre drills (for example ISO 2540, ISO 2541, ISO 866).
- Symbol rules (Annex B):
- Symbol and complement proportions are defined for harmonization with other drawing inscriptions.
- Line thickness for symbol outlines (d’) is typically 1/10 of the lettering height.
- Numerals and letters for centre‑hole specifications use the same lettering style and size as dimensioning (ISO 3098/1).
- Minimum recommended spacing between adjacent lines is 0.7 mm.
Applications and users
- Practical for mechanical drafters, design engineers, manufacturing engineers, CNC programmers and quality inspectors who need:
- Clear, compact drawing notation for centre holes.
- Consistent interpretation of centre‑hole requirements without drawing full detailed geometry.
- Useful in production drawings, assembly drawings and standards‑based documentation where standardized centre drills are used.
Related standards
Keywords: ISO 6411, centre holes, technical drawings, simplified representation, drawing symbols, centre hole designation, Annex A, Annex B.
