Overview
EN ISO 6433:2012 - Technical product documentation - Part references specifies rules for presenting part references (position numbers) on assembly representations such as assembly drawings and exploded views. Its purpose is to ensure clear, unambiguous identification of constituent parts in the related parts list (parts list / BOM). This harmonized CEN/ISO standard aligns drawing conventions across design, manufacturing and documentation teams.
Key topics and requirements
- Scope and purpose: Defines how part references are shown on assembly drawings to link each part to a parts list (see ISO 7573).
- Identifiers: Preferably use numerals only; capital letters may augment if necessary. Recommended maximum of three characters for part reference numbers. Characters must comply with ISO 3098-0 lettering.
- Appearance: All references on a drawing must be uniform in type and height and be clearly distinguishable from other annotations. Typical methods include:
- Encircling the part reference with a continuous narrow line (ISO 128 line type 01.1).
- Using larger character height (for example, larger than dimension text).
- Location and leader lines: Part references must be placed outside part outlines and connected to the part by a leader line that complies with ISO 128-22. Leader lines should not intersect and should be short and angled for clarity.
- Identical parts: Identical components should carry the same part reference and need only be indicated once on the drawing unless ambiguity requires repetition (see Annex A).
- Positioning: Arrange part references in horizontal rows and/or vertical columns where possible to maintain legibility; multiple references sharing a leader line may be grouped.
- Numbering sequence: Adopt a clear numbering sequence (e.g., assembly order, component importance, or another logical order).
- Annex A: Rules for indicating number of parts (use of “×” in line with ISO 129-1) and repeating encircled references when required.
Applications and users
EN ISO 6433:2012 is used by:
- Mechanical designers, CAD technicians and draughtsmen preparing assembly drawings
- Technical illustrators and documentation specialists creating exploded views and manuals
- Manufacturing, procurement and maintenance teams that rely on accurate parts lists (BOMs)
- Quality assurance and standardization teams implementing drawing conventions
Practical benefits include improved clarity of assembly documentation, reduced errors in parts ordering and manufacturing, and consistent cross-team communication.
Related standards
Normative references that should be used alongside EN ISO 6433:2012:
Keywords: EN ISO 6433:2012, part references, assembly drawings, technical product documentation, parts list, leader lines, ISO 6433.
