Blueprints are easier to read without repetitive +/−positive / minus values on every line.
— The industry standard for most machined parts. c (coarse) v (very coarse) Table 1: Permissible Deviations for Linear Dimensions (mm) Nominal Length Range (mm) m (medium) c (coarse) v (very coarse) 0.5 up to 3 over 3 up to 6 over 6 up to 30 over 30 up to 120 over 120 up to 400 over 400 up to 1000 Source: ZEISS Quality Forum ISO 2768 PDF . Part 2: Geometrical Tolerances (ISO 2768-2) ISO 2768 Tolerance Standards for CNC Machining - JLCCNC
In high-precision industries like CNC machining and sheet metal fabrication, specifying exact tolerances for every dimension is time-consuming and often unnecessary.
Saves design time since engineers do not need to calculate individual tolerances for non-critical features. iso 2768 general tolerances pdf exclusive
Engineers and machinists rely on specific tables within the standard to determine the exact numerical values allowed for a given dimension. Linear Dimensions (ISO 2768-1)
Angular tolerances are determined based on the length of the shorter leg of the angle in question. Nominal Length Range (mm) Class f (Fine) Class m (Medium) Class c (Coarse) Class v (Very Coarse) Over 10 to 50 Over 50 to 120 Over 120 to 400 Over 400 Geometric Tolerance Values (ISO 2768-2)
| Nominal Length of Longer Element (mm) | H | K | L | | :--- | :--- | :--- | :--- | | up to 100 | 0.5 | 0.6 | 0.6 | | over 100 up to 300 | 0.5 | 0.6 | 1.0 | | over 300 up to 1000 | 0.5 | 0.8 | 1.5 | | over 1000 up to 3000 | 0.5 | 1.0 | 2.0 | Part 2: Geometrical Tolerances (ISO 2768-2) ISO 2768
The ISO 2768 standard is available in a PDF format, which provides a comprehensive guide to the general tolerances for various types of dimensions. The PDF document outlines the tolerance classes, tolerance values, and application guidelines for linear and angular dimensions.
: Values range from 0.02mm (H) to 0.6mm (L) for lengths up to 100mm.
To utilize ISO 2768, a designer must include a specific note in the title block of the engineering drawing. The recommended notation format is: When a drawing states “ISO 2768-mK
This paper aims to dissect the utility of the ISO 2768 standard while addressing the specific keyword of exclusivity regarding its distribution. As an international standard, the document is protected by copyright, making official PDF versions an "exclusive" product often restricted behind paywalls. This creates a dichotomy between the standard's widespread necessity and its restricted accessibility.
: Usually indicated in or near the title block of a drawing (e.g., ISO 2768-m Part 2: Geometrical Tolerances (ISO 2768-2)
As detailed in the standard’s two parts (ISO 2768-1 for linear/angular dimensions and ISO 2768-2 for geometrical features), the core principle is that of default acceptance criteria . When a drawing states “ISO 2768-mK,” it signals that any dimension not explicitly toleranced must comply with the “medium” (m) class for size and the “K” class for geometry. This eliminates the need to clutter a drawing with dozens of redundant ±0.1 mm notes. The PDFs of this standard reveal a carefully calibrated matrix: for a nominal range of 6 to 30 mm, the “fine” (f) class permits ±0.2 mm, while the “coarse” (c) class allows ±0.8 mm. These are not arbitrary numbers but are derived from statistical process controls and common workshop capabilities.