| Class | Code | Use case | |-------|------|----------| | | Fine | High precision (e.g., instruments) | | m | Medium | General machining (most common) | | c | Coarse | Fabrication, welding | | v | Very coarse | Castings, rough forgings |
This small notation can save a significant amount of time and prevents misinterpretation.
| Class | Description | Typical Application | | :--- | :--- | :--- | | | Fine | Precision engineering, small electronic components. | | m | Medium | General machinery, standard CNC parts. (Most common) | | c | Coarse | Fabricated parts, welded assemblies, castings. | | v | Very Coarse | Rough structural components, sheet metal work. |
In the PMI (Product Manufacturing Information) data, add a general tolerance annotation in the metadata referencing "ISO 2768-mH".
Selecting the appropriate tolerance class is a critical design decision that balances precision requirements against manufacturing cost and feasibility.
This table applies to external dimensions (e.g., shaft diameter), internal dimensions (e.g., hole diameter), and step dimensions.
Permissible deviations for broken edges:
It applies when a designer does write a specific tolerance next to a dimension. Instead, the drawing notes "ISO 2768" or "General tolerances ISO 2768-mK" (or similar) in the title block.
This comprehensive guide breaks down the ISO 2768 standard, its parts, tolerance classes, and how downloading an ISO 2768 General Tolerances PDF can optimize your manufacturing workflow. What is ISO 2768?
Below are simplified reference tables commonly found in an ISO 2768 PDF. They illustrate how permissible variations scale based on the size of the dimension. Linear Dimensions (ISO 2768-1)
