1.0What is ISO 2768?
1.1A Comprehensive Overview of the Standard and Its Applications
ISO 2768 is not just another standard—it is a globally recognized framework for general tolerances of linear and angular dimensions. It provides a unified specification for dimensional tolerances in manufacturing, ensuring product quality and consistency across production.
1.2Linear vs. Angular Dimensions
Linear dimensions refer to measurements such as length, width, and height.
Angular dimensions involve angles—such as the bend in a metal sheet or the tilt of a mechanical component.
Precision in these dimensions is critical. Even the slightest deviation can lead to malfunction or safety risks. ISO 2768 defines acceptable tolerance ranges to ensure that parts function as intended.
For instance, a component designed with a length of 100 mm might be allowed to vary between 99.95 mm and 100.05 mm under ISO 2768, maintaining both safety and functionality.
1.3Structure and Classification
Published by the International Organization for Standardization (ISO), ISO 2768 consists of two main parts:
- ISO 2768-1 covers general tolerances for linear and angular dimensions. When dimensions are shown on a technical drawing without specific tolerances, this standard applies the appropriate tolerance grade automatically.
- ISO 2768-2 addresses general tolerances for features without individual tolerance indications, such as straightness, flatness, perpendicularity, and run-out.
1.4Tolerance Grades
ISO 2768-1 defines four tolerance grades for linear and angular dimensions:
- f (fine)
- m (medium)
- c (coarse)
- v (very coarse)
These grades accommodate various manufacturing needs and precision levels.
ISO 2768-2 introduces three grades for geometrical tolerances:
- H (high precision)
- K (medium precision)
- L (low precision)
These are used to classify the accuracy of form and position features.
1.5Why ISO 2768 Matters
ISO 2768 is widely used across industries such as mechanical engineering, CNC machining, and metal fabrication. It’s a standardized approach:
- Reduces miscommunication between design and manufacturing teams
- Prevents production issues caused by tolerance misinterpretation
- Ensures product consistency and reliability
- Facilitates collaboration between global manufacturers and clients
In Germany, ISO 2768 is also implemented under the DIN standard, further supporting uniform execution.
1.6Surface Roughness Considerations
While ISO 2768 focuses on dimensional tolerances, it also addresses surface roughness by defining levels of finish quality. These classifications help standardize expectations across different manufacturing methods and ensure functional, consistent surface treatment.
1.7Example Tolerances for CNC Metal Machined Parts
| Feature | Dimension Range (mm) | Tolerance (± mm) | Note |
| Linear Dimensions | 0.5 – 6 | ±0.05 | Small features |
| >6 – 30 | ±0.10 | General-purpose parts | |
| >30 – 120 | ±0.15 | Medium-sized parts | |
| >120 – 400 | ±0.25 | Large machined features | |
| Hole Diameter | ≤6 | ±0.05 | High precision required |
| >6 – 30 | ±0.10 | For standard fasteners | |
| >30 – 100 | ±0.15 | Medium-size holes | |
| Flatness | ≤100 | 0.1 | Base surface flatness |
| >100 | 0.2 | Larger flat surfaces | |
| Straightness | ≤100 | 0.1 | For shafts or long features |
| >100 | 0.2 | ||
| Perpendicularity | ≤100 | 0.2 | Between walls or mating parts |
| >100 | 0.3 | ||
| Position Tolerance | ≤100 | 0.5 | Hole or feature position |
| Roundness / Cylindricity | ≤50 | 0.1 – 0.2 | For rotating or mating parts |
2.0The Purpose and Importance of ISO 2768
2.1Why ISO 2768 Is Used
ISO 2768 provides a standardized system of general tolerances for linear dimensions, angular dimensions, and certain geometrical features. This reduces the need for designers to specify individual tolerances for every feature on a technical drawing.
This is particularly beneficial in complex assemblies involving multiple components, as it:
- Saves design time
- Reduces drawing complexity
- Minimizes errors in interpreting technical drawings
For example, critical features such as external radii or chamfer heights can follow the general tolerances outlined in ISO 2768. This simplifies communication between designers, engineers, and manufacturers—ultimately improving manufacturing efficiency.
2.2The Role of Tolerances in Manufacturing and Quality Control
- Defining acceptable deviation: Tolerances specify how much a part’s size or geometry can vary from the nominal value, ensuring the part still meets design intent.
- Ensuring assembly quality: Proper tolerances ensure parts fit and function correctly during assembly, reducing the risk of rework or failure.
- Controlling production costs: Applying reasonable tolerances avoids excessive machining and over-engineering, which helps lower manufacturing expenses.
- Streamlining communication: A standardized tolerance framework helps align expectations between designers and manufacturers, minimizing misinterpretation.
- Without clearly defined tolerances, even small dimensional variations can result in poor fit, compromised quality, or product failure in the field.
2.3Why ISO 2768 Matters in Modern Manufacturing
- Simplifies engineering drawings and enhances communication between designers, engineers, and production teams
- Supports global consistency, ensuring compatibility and interchangeability of components produced in different regions
- Enables international collaborationby providing a shared understanding of tolerance requirements, eliminating confusion caused by local standards
- Improves product quality and reliabilityby reducing manufacturing errors and supporting consistent performance across production runs
ISO 2768 is a cornerstone of efficient, standardized manufacturing—offering a balance between precision, practicality, and global interoperability.
2.4How to Select the Right ISO 2768 Tolerance Grade
Choosing the appropriate ISO 2768 tolerance grade requires careful consideration of several key factors. Selecting the right grade ensures a balance between product functionality, manufacturing cost, and feasibility.
| Factor | Description |
| Part Function | Critical components—such as those in engines or medical devices—require fine tolerances. Non-critical parts may use coarse tolerances. |
| Cost Control | Tighter tolerances increase machining complexity and cost. Reasonable tolerances help reduce manufacturing expenses. |
| Design Complexity | Complex geometries often necessitate finer tolerances to ensure accuracy. Simpler parts can tolerate looser grades. |
| Material Properties | Certain materials demand stricter control to maintain stability and performance during processing. |
For most general engineering applications, the medium (m) tolerance grade is considered a practical default—it strikes a good balance between precision and cost-efficiency.
The table below offers guidance on typical use cases, outlining recommended tolerance standards (ISO 2768 and ISO 286) based on part function and application requirements:
| Application | Description | ISO 2768 Tolerance Class | ISO 286 Grade | Reason for Tolerance Choice |
| Precision machined parts | High-precision parts for aerospace, automotive, or medical use. | Fine | IT6 or tighter | Ensures minimal deviation in size and fit for high-accuracy assemblies. |
| Interchangeable mechanical parts | Replaceable parts such as gears, bearings, fasteners in assemblies. | Fine | IT7 or tighter | Supports dimensional consistency and standardized fits between components. |
| General mechanical assemblies | Standard machinery parts like housings, frames, or brackets. | Medium | – | Balances manufacturing cost and dimensional accuracy. |
| Large fabricated structures | Welded or assembled structures such as frames, beams, and plates. | Medium | – | Suitable for larger parts where tight tolerances are impractical. |
| Plastic components | Molded or machined plastic parts with moderate tolerance requirements. | Medium | IT8 or looser | Accommodates material shrinkage and lower dimensional stability. |
| Shafts and holes for rotating parts | Rotating elements requiring functional fits and alignment. | Fine | IT6–IT7 | Ensures precise circular fits and maintains rotational balance. |
| Sheet metal parts | Bended or punched components like panels, enclosures, or covers. | Medium | – | Appropriate for sheet forming methods with natural variability. |
| Electrical enclosures and casings | Non-precision covers for electrical or electronic systems. | Medium | – | Provides sufficient fit for assembly without excessive manufacturing cost. |
| Consumer product components | Plastic or light metal parts in electronics or home appliances. | Medium | IT8 | Prioritizes manufacturability and cosmetic fit over tight tolerances. |
Application of ISO 2768 and ISO 286 Tolerances in Engineering
2.5What Does ISO 2768-mK Mean?
ISO 2768-mK refers to a specific combination of general tolerance grades under the ISO 2768 standard. It is commonly used in manufacturing scenarios that require moderate dimensional accuracy—typically in the millimeter range—along with standard control over geometrical features.
2.6Breaking Down “mK”
“m” — Medium Tolerance Grade
The letter “m” stands for medium, which is one of the four linear and angular dimensional tolerance grades defined in ISO 2768-1:
- f– fine
- m– medium
- c– coarse
- v– very coarse
The medium grade allows for moderate dimensional variation, suitable for most general engineering applications where tight tolerances are not critical but consistency is still essential.
“K” — Geometrical Tolerance Grade
The “K” refers to a geometrical tolerance class, as defined in ISO 2768-2. It applies to form and positional tolerances of features such as:
- Straightness
- Flatness
- Perpendicularity
- Run-out
The K grade represents a medium level of geometrical control, offering a balanced approach between precision and manufacturing practicality.
In summary, ISO 2768-mK is a widely used specification for components that require moderate dimensional precision and standard geometric control. It simplifies technical drawings while maintaining essential quality and functional integrity in manufacturing.
3.0ISO 2768-1: General Tolerances for Linear and Angular Dimensions
ISO 2768-1 simplifies technical drawings by defining general tolerances for linear and angular dimensions, eliminating the need to specify individual tolerances for every feature. It is especially useful for standard machined parts where specific tolerances are not explicitly indicated.
This standard applies to:
- External and internal dimensions
- Step distances
- Diameters and radii
- Hole spacings and edge distances
- External radii and chamfer heights (e.g., broken edges)
3.1Tolerance Classes and Their Applications
ISO 2768-1 defines four tolerance classes based on the required precision level. Selecting the appropriate class depends on functional requirements, manufacturing capability, and cost considerations.
| Tolerance Class | Description | Typical Applications |
| f (fine) | High-precision tolerance | Precision-machined components, instrumentation |
| m (medium) | Standard general-purpose tolerance | Mechanical parts with moderate accuracy requirements |
| c (coarse) | For low-precision components | Structural parts, welded assemblies |
| v (very coarse) | For rough or initial machining | Flame-cut profiles, raw structural elements |
The medium (m) class is commonly used for general engineering applications, offering a good balance between precision and cost-effectiveness.
3.2Table 1 General Tolerances for Linear Dimensions (Unit: mm)
| Nominal Length Range (mm) | f (fine) | m (medium) | c (coarse) | v (very coarse) |
| 0.5 up to 3 | ±0.05 | ±0.1 | ±0.2 | – |
| Over 3 up to 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| Over 6 up to 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 |
| Over 30 up to 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 |
| Over 120 up to 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 |
| Over 400 up to 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 |
| Over 1000 up to 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 |
| Over 2000 up to 4000 | – | ±2.0 | ±4.0 | ±8.0 |
Based on tolerance class and nominal length range — Reference: ISO 2768-1
3.3Table 2 – External Radii and Chamfer Heights
| Permissible deviations in mm for ranges in nominal lengths | Tolerance Class Designation (Description) | |||
| f (fine) | m (medium) | c (coarse) | v (very coarse) | |
| 0.5 up to 3 | ±02 | ±0.2 | ±0.4 | ±0.4 |
| over 3 up to 6 | ±0.5 | ±0.5 | ±1.0 | ±1.0 |
| over 6 | ±1.0 | ±1.0 | ±2.0 | ±2.0 |
NOTE: Likewise, tolerances below 0.5 mm should be noted next to the relevant dimension.
3.4Table 3 – Angular Dimensions
| Permissible deviations in mm for ranges in nominal lengths | Tolerance Class Designation (Description) | |||
| f (fine) | m (medium) | c (coarse) | v (very coarse) | |
| up to 10 | ±1º | ±1º | ±1º30′ | ±3º |
| over 10 up to 50 | ±0º30′ | ±0º30′ | ±1º | ±2º |
| over 50 up to 120 | ±0º20′ | ±0º20′ | ±0º30′ | ±1º |
| over 120 up to 400 | ±0º10′ | ±0º10′ | ±0º15′ | ±0º30′ |
| over 400 | ±0º5′ | ±0º5′ | ±0º10′ | ±0º20′ |
Table 3 defines general tolerances for angles/angular dimensions. It should be noted that the tolerance units for angles are degrees and minutes.
3.5Application of ISO 2768-1
ISO 2768-1 applies to:
Linear dimensions without individual tolerance indications, such as:
- External and internal lengths
- Widths, heights, and thicknesses
- Hole diameters and shaft diameters
Angular dimensions, including:
- Angles between surfaces
- Chamfers and bevels
Features produced by common manufacturing processes, such as:
- Machining
- Cutting
- Bending
- Stamping
- Assembly and welding
This standard is typically applied to metal and plastic parts in general mechanical engineering drawings.
4.0ISO 2768-2: General Geometrical Tolerances
ISO 2768-2 sets general geometrical tolerances for features like straightness, flatness, roundness, and cylindricity, simplifying drawings by avoiding detailed tolerance marks.
It mainly applies to parts made by material removal processes (e.g., milling, turning) and classifies tolerances into three levels:
- H– High precision
- K– Medium precision
- L– Low precision
Unlike dimensional tolerance standards (like ISO 286), ISO 2768-2 controls geometry using tolerance zones—areas between two parallel planes or surfaces where the actual feature must lie. This method accounts for surface roughness and minor variations during measurement but keeps deviations within acceptable limits.
The standard provides tables covering tolerances for:
- Straightness and flatness
- Circularity and cylindricity
- Perpendicularity, angularity, parallelism
- Run-out and total run-out
Each tolerance depends on the feature’s nominal size and chosen precision class (H, K, or L).
4.1Table 4 – General Tolerances on Straightness and Flatness
| Ranges of nominal lengths in mm | Tolerance Class | ||
| H | K | L | |
| up to 10 | 0.02 | 0.05 | 0.1 |
| above 10 to 30 | 0.05 | 0.1 | 0.2 |
| above 30 to 100 | 0.1 | 0.2 | 0.4 |
| above 100 to 300 | 0.2 | 0.4 | 0.8 |
| above 300 to 1000 | 0.3 | 0.6 | 1.2 |
| above 1000 to 3000 | 0.4 | 0.8 | 1.6 |
Table 4 defines flatness and straightness tolerance classes. Taking the compressor example again, the contact surface between the compressor and the base and the contact surface between the base and the engine are important, so their flatness tolerances are specified in the drawings. Straightness tolerance refers to the degree of variation within a specified straight line on that surface. Another use is to allow for the degree of bending or twisting of the axis of a part.
4.2Table 5 – General Tolerances on Perpendicularity
| Ranges of nominal lengths in mm | Tolerance Class | ||
| H | K | L | |
| up to 100 | 0.2 | 0.4 | 0.6 |
| above 100 to 300 | 0.3 | 0.6 | 1.0 |
| above 300 to 1000 | 0.4 | 0.8 | 1.5 |
| above 1000 to 3000 | 0.5 | 1.0 | 2.0 |
Verticality distance is in millimeters. Similar to flatness, we define the gap between two planes to be less than the allowable deviation in Table 5. Our goal is to achieve a 90 degree angle.
4.3Table 6 – General Tolerances on Symmetry
| Ranges of nominal lengths in mm | Tolerance Class | ||
| H | K | L | |
| up to 100 | 0.5 | 0.6 | 0.6 |
| above 100 to 300 | 0.5 | 0.6 | 1.0 |
| above 300 to 1000 | 0.5 | 0.8 | 1.5 |
| above 1000 to 3000 | 0.5 | 1.0 | 2.0 |
Table 6 shows the symmetry tolerances on the part on the datum plane.
4.4Table 7 – General Tolerances on Circular Run-Out
| Ranges of nominal lengths in mm | Tolerance Class | ||
| H | K | L | |
| 0.1 | 0.2 | 0.5 | |
This universal tolerance allows the designer to choose the tolerance level that best suits the requirements. For example, if the part is to be used in a CNC project with tight tolerance requirements, it would be wise to choose a smaller tolerance range. Conversely, if high-volume parts are manufactured for lower tolerance applications, a wider tolerance range will be more cost-effective.
4.5Common Applications of ISO 2768-2
| Application Area | Description | Example |
| Sheet Metal Fabrication | Geometric control for parts without specific tolerance marks | Flatness, straightness, perpendicularity in sheet metal parts |
| Mechanical Components | Control of geometric relations at mating or assembly surfaces | Axial runout of gear shafts, symmetry of keyways |
| Welded Structures | Shape and positional consistency of large welded assemblies | Parallelism and perpendicularity of welded frames |
| Machined Parts (Non-critical) | Basic form control where high precision is not required | Geometry control for shims, brackets, flanges |
| Injection Molding/Casting | Basic geometric control of molded parts | Flatness, symmetry, and positioning of housings |
| Assembly Guide or Mating Surfaces | Ensuring basic positional accuracy between parts | Positioning of guide pins, dowel holes |
| Non-functional Reference or Auxiliary Surfaces | Control for appearance or assembly quality rather than function | Straightness of housing sidewalls, perpendicularity of decorative parts |
5.0Download Official ISO 2768 Tolerance Standards:
General Tolerance Standard ISO 2768-1 (Linear & Angular Dimensions) .pdf
General Tolerance Standard ISO 2768-2 (Geometrical Tolerances) .pdf
6.0Summary
ISO 2768 defines general tolerances widely used in manufacturing to simplify design and production.
- ISO 2768-1 covers linear and angular dimensions with general tolerance classes.
- ISO 2768-2 ensures accuracy of geometric features such as straightness, perpendicularity, and symmetry, critical for proper part assembly.
When selecting standards, consider:
- The required dimensional accuracy of the product
- The need to maintain geometric relationships between parts
In practice, ISO 2768-1 and ISO 2768-2 are often combined. For example, automotive engine components typically require the dimensional precision of ISO 2768-1 along with geometric control per ISO 2768-2 to guarantee overall performance and assembly quality.
- ISO 2768-2 is used alongside ISO 2768-1 to form a complete general tolerance scheme.
- It reduces redundant tolerance markings, improving drawing clarity.
- For CNC and mold processing requiring moderate geometric precision, the K (medium)tolerance class is commonly selected.
7.0ISO 2768 Frequently Asked Questions (FAQ)
What is the difference between ISO 2768 and ISO 286?
ISO 2768 specifies general tolerances for linear and angular dimensions, applicable to various parts; whereas ISO 286 focuses on specific tolerances for cylindrical fits such as shafts and holes, especially for interference or clearance fits. Therefore, ISO 286 is suitable for precise fit scenarios, while ISO 2768 is used for more general tolerance control.
How does ISO 2768 differ from ASME Y14.5?
ISO 2768 is an international standard providing general tolerance grades; ASME Y14.5 is a U.S. standard focusing on GD&T (Geometric Dimensioning and Tolerancing), covering more complex geometric tolerances such as straightness, flatness, etc. ISO 2768 is suitable for general dimensional tolerances, while ASME Y14.5 is applied to highly detailed and complex design requirements.
What is the relationship between ISO 2768 and DIN standards?
DIN standards are widely used in Germany and Europe, similar to ISO 2768, but may include stricter or process-specific tolerance limits (e.g., for sheet metal, injection molding). DIN also provides more detailed application guidance to meet European manufacturing needs.
How to conduct ISO 2768 compliance audit?
Compliance audit requires systematically reviewing manufacturing processes and drawings to verify that linear and angular tolerances conform to ISO 2768, especially tolerance grades (H, K, L) and geometric features (such as straightness, flatness, perpendicularity). Focus on matching tolerance annotations on drawings with manufacturing processes to ensure parts meet specifications.
What are common pitfalls in ISO 2768 compliance audits?
Main pitfalls include misunderstanding or incorrect application of drawing tolerances, ignoring tolerances for critical features (such as external radii, chamfers), and improper execution of tolerance grades. Lack of understanding of manufacturing process applicability can also lead to non-compliance.
How to obtain ISO 2768 certification?
The certification process includes:
- Understanding and mastering the requirements of ISO 2768;
- Conducting a gap analysis to identify differences between current processes and the standard;
- Implementing necessary changes, including updates to drawings, tolerance grades, and process adjustments;
- Performing internal audits to verify the effectiveness of changes and team awareness;
- Selecting an ISO-accredited certification body for external audit;
- Obtaining certification and maintaining ongoing compliance through regular review and improvement.
References
https://www.fictiv.com/articles/iso-2768-an-international-standard
https://xometry.pro/en/articles/standard-tolerances-manufacturing/