Overview of ISO 2768
ISO 2768 defines general tolerances for linear and angular dimensions when no specific tolerances are indicated on engineering drawings. It helps reduce drawing complexity by avoiding the need to specify individual tolerances for every dimension.
The “mK” designation combines medium (m) tolerance class for linear dimensions and K class for geometrical tolerances. These tables are widely used by engineers to quickly determine whether a part is within acceptable limits without detailed specifications.
General Tolerance Table (ISO 2768-1, Class m)
Linear Dimensions (mm)
0.5 – 3
±0.1
3 – 6
±0.1
6 – 30
±0.2
30 – 120
±0.3
120 – 400
±0.5
400 – 1000
±0.8
1000 – 2000
±1.2
Geometrical Tolerances (ISO 2768-2, Class K)
Straightness / Flatness
Medium
Perpendicularity
Medium
Symmetry
Medium
Circular Runout
Medium
(Note: Exact values depend on feature size and are defined in ISO 2768-2 tables.)(Note: Exact values depend on feature size and are defined in ISO 2768-2 tables.)
Core Concepts
General Tolerances
Tolerance Classes (f, m, c, v)
Geometrical Classes (H, K, L)
High-Cost Errors
Assuming Incorrect Tolerance Class
Using the wrong class (e.g., m instead of f) results in parts being out of spec or over-engineered.
Applying ISO 2768 Where It Doesn’t Apply
Using general tolerances for critical features can cause functional failures and assembly issues.
How to Apply ISO 2768
01
Confirm Standard Usage
02
Identify Tolerance Class
Check whether the drawing uses f, m, c, or v (e.g., mK).
03
Reference the Tables
04
Apply Geometrical Class
05
Validate Critical Features
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Comparison & Related Standards
ISO 2768
A traditional general tolerance standard widely used for simplifying drawings and reducing specification effort.
ISO 22081
A modern standard designed to replace ISO 2768, offering more precise and flexible tolerancing methods.