ISO 2768: The Ultimate Guide to General Tolerances for Machined Parts

Precision is critical in manufacturing, but how do companies ensure accuracy without over-complicating designs? Enter ISO 2768.

ISO 2768 provides general tolerances for machined parts, simplifying technical drawings and boosting manufacturing efficiency. Tolerances are crucial for controlling part dimensions and ensuring functionality.

This guide covers ISO 2768's two parts: linear/angular tolerances (Part 1) and geometrical tolerances (Part 2). You'll learn how these standards help reduce errors, cut costs, and improve product quality.

In this post, we’ll explain why ISO 2768 matters and how it streamlines global manufacturing processes.

What is ISO 2768?

ISO 2768 (also known as ISO2768 or DIN ISO 2768) is an international standard that revolutionizes machining tolerances and simplifies technical drawings. This comprehensive standard tolerance system provides general tolerances for linear and angular dimensions, making it essential for CNC machining tolerances and standard machining tolerances in mm.

Core Components

The standard consists of two fundamental parts, defining both general tolerancing and specific tolerance requirements:

1. ISO 2768-1: Controls linear and angular dimensions through four tolerance classes based on the ISO tolerance chart:

• Fine tolerance (f)

• Medium ISO (m) / ISO 2768 mittel

• Coarse (c)

• Very coarse (v)

2. ISO 2768-2: Manages geometric tolerance standards through three classes:

• H class

• K class

• L class

Common combinations include ISO 2768-mk, ISO 2768-ml, and ISO 2768-m, with ISO 2768 mk tolerance being particularly popular in machine tolerance applications.

Primary Purpose

ISO 2768 serves multiple essential functions in manufacturing:

• Streamlines technical drawing specifications by eliminating individual tolerance annotations

• Ensures consistent production quality across global manufacturing facilities

• Reduces production costs through standardized tolerance specifications

• Facilitates international collaboration between manufacturing partners

• Minimizes design misinterpretations through unified tolerance guidelines

Industry Applications

Manufacturing Sectors

The standard finds extensive application across diverse industries:

1. CNC Machining

1. Ensures precision manufacturing for complex mechanical components and assemblies

2. Maintains consistent quality standards across high-volume production runs

3. Enables accurate toolpath calculations based on standardized tolerance ranges

2. Tooling and Mold-Making

1. Guarantees precise fit between mold components and final products

2. Establishes uniform standards for tool wear compensation

3. Maintains dimensional stability across multiple production cycles

3. Architecture and Construction

1. Standardizes structural component tolerances for improved building assembly

2. Ensures proper fit between prefabricated construction elements

3. Maintains safety standards through precise dimensional control

4. General Manufacturing

1. Optimizes production processes through standardized quality control measures

2. Reduces waste by establishing clear acceptance criteria

3. Improves product consistency across different manufacturing locations

5. Industrial Design

1. Guides designers in creating manufacturable products meeting quality standards

2. Facilitates communication between design and production teams

3. Enables accurate prototyping and product development cycles

ISO 2768 Part 1: Linear and Angular Dimensions

ISO 2768-1 provides general tolerances for linear and angular dimensions, eliminating the need to individually specify tolerances for each feature. It covers a wide range of dimensions, such as external sizes, radii, diameters, and chamfers. By using standardized tolerances, manufacturers reduce errors and improve production efficiency while maintaining part functionality.

Overview of ISO 2768-1

This fundamental part addresses multiple dimensional aspects:

• External dimensions controlling overall component size specifications

• Internal dimensions defining holes, slots, and internal features

• Step sizes determining incremental dimensional changes

• Diameters specifying circular feature measurements

• Distances establishing spacing between features

• External radii defining curved surface specifications

• Chamfer heights controlling edge modifications

Tolerance Classifications

ISO 2768-1 introduces four distinct tolerance classes, each serving specific precision requirements:

Fine (f) Tolerance

• Delivers highest precision suitable for high-accuracy mechanical components

• Supports critical assemblies requiring minimal dimensional variation

• Enables precise fit between interacting mechanical elements

Medium (m) Tolerance

• Provides balanced precision for standard manufacturing processes

• Offers cost-effective solution for general mechanical applications

• Maintains reasonable dimensional control without excessive cost

Coarse (c) Tolerance

• Suits components without strict dimensional requirements

• Reduces manufacturing costs through relaxed specifications

• Supports high-volume production scenarios

Very Coarse (v) Tolerance

• Accommodates non-critical dimensional requirements

• Maximizes manufacturing efficiency through broader tolerances

• Minimizes production costs for basic components

Linear Dimension Specifications

Nominal Size Range (mm)	Fine (f)	Medium (m)	Coarse (c)	Very Coarse (v)
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

These specifications enable manufacturers to:

• Select appropriate tolerances based on functional requirements

• Balance precision against manufacturing costs

• Maintain consistent quality across production runs

External Radii and Chamfer Heights

The standard defines specific tolerances for curved features:

Size Range (mm)	Fine/Medium (±mm)	Coarse/Very Coarse (±mm)
0.5-3	±0.2	±0.4
3-6	±0.5	±1.0
>6	±1.0	±2.0

Key implementation considerations include:

• Surface finish requirements affect achievable tolerances

• Manufacturing method influences tolerance selection

• Material properties impact dimensional stability

Angular Dimension Control

Angular tolerances follow distinct measurement criteria:

Length Range (mm)	Fine/Medium	Coarse	Very Coarse
≤10	±1°	±1°30′	±3°
10-50	±0°30′	±1°	±2°
50-120	±0°20′	±0°30′	±1°
120-400	±0°10′	±0°15′	±0°30′

These specifications ensure:

• Precise angular relationships between features

• Consistent assembly alignment

• Proper functional performance of mating components

ISO 2768 Part 2: Geometrical Tolerances for Features

ISO 2768-2 provides guidelines for general geometrical tolerances without individual specifications on drawings. It covers important features such as flatness, straightness, perpendicularity, symmetry, and circular run-out. By standardizing these tolerances, manufacturers ensure parts meet functional requirements while reducing design complexity and production costs.

Overview of ISO 2768-2

The standard addresses critical geometric characteristics:

• Surface flatness specifications for optimal component interface performance

• Straightness requirements ensuring proper alignment in assemblies

• Perpendicularity controls for precise angular relationships

• Symmetry specifications maintaining balanced feature distribution

• Circular run-out limits controlling rotational accuracy

Tolerance Classifications

ISO 2768-2 defines three tolerance classes based on precision requirements:

H-Class Tolerance

• Provides highest precision control for critical geometric features

• Ensures exceptional accuracy in high-performance applications

• Maintains strict conformance to geometric design intent

K-Class Tolerance

• Offers balanced precision for standard manufacturing processes

• Delivers cost-effective geometric control in general applications

• Supports efficient production while maintaining quality standards

L-Class Tolerance

• Allows wider geometric variations for non-critical features

• Reduces manufacturing costs through relaxed specifications

• Maintains basic functionality while maximizing production efficiency

Straightness and Flatness Specifications

Nominal Length (mm)	H (mm)	K (mm)	L (mm)
≤10	0.02	0.05	0.1
10-30	0.05	0.1	0.2
30-100	0.1	0.2	0.4
100-300	0.2	0.4	0.8
300-1000	0.3	0.6	1.2
1000-3000	0.4	0.8	1.6

Implementation considerations:

• Surface finish impacts achievable flatness tolerances

• Manufacturing method influences straightness control capabilities

• Material properties affect geometric stability

Perpendicularity Control

Length (mm)	H (mm)	K (mm)	L (mm)
≤100	0.2	0.4	0.6
100-300	0.3	0.6	1.0
300-1000	0.4	0.8	1.5
1000-3000	0.5	1.0	2.0

Key applications include:

• Critical alignment requirements between mating components

• Structural element orientation control

• Assembly reference surface specifications

Symmetry Requirements

Length (mm)	H (mm)	K (mm)	L (mm)
≤100	0.5	0.6	0.6
100-300	0.5	0.6	1.0
300-1000	0.5	0.8	1.5
1000-3000	0.5	1.0	2.0

Essential considerations:

• Feature distribution across reference planes

• Balance requirements for rotating components

• Aesthetic specifications for visible surfaces

Circular Run-out Parameters

Tolerance Class	Maximum Deviation (mm)
H	0.1
K	0.2
L	0.5

Critical applications:

• Rotating component precision control

• Bearing surface specifications

• Shaft alignment requirements

Implementation Guidelines

To maximize effectiveness:

1. Select appropriate tolerance classes based on functional requirements

2. Consider manufacturing capabilities when specifying geometrical tolerances

3. Balance precision requirements against production costs

4. Document special requirements exceeding standard specifications

5. Maintain consistent measurement protocols across production

Through systematic implementation of ISO 2768-2, manufacturers can:

• Achieve optimal geometric control

• Maintain consistent quality standards

• Reduce inspection complexity

• Streamline production processes

• Ensure component interchangeability

These geometric tolerances provide essential controls for maintaining product quality while optimizing manufacturing efficiency across diverse industrial applications.

How to Apply ISO 2768 to Technical Drawings

Engineering drawings require precise tolerance specifications to ensure successful manufacturing outcomes. ISO 2768 provides standardized guidelines for defining acceptable dimensional variations. Understanding these requirements enables engineers to optimize both product quality and production costs.

Importance of Tolerance Specification

Proper tolerance specification directly impacts multiple aspects of manufacturing success. Engineers must balance precision requirements against production capabilities. Clear documentation prevents costly manufacturing errors while streamlining quality control processes.

Manufacturing teams rely on accurate tolerance information to:

• Establish appropriate machining parameters based on specified dimensional requirements

• Select suitable measurement tools and inspection methods for quality verification

• Determine acceptable production variations without compromising product functionality

• Control manufacturing costs through optimized tolerance specifications

Compressor Base Case Study

A vehicle engine compressor base demonstrates effective ISO 2768 implementation. This component connects an AC compressor to the engine block, requiring careful consideration of various tolerance requirements.

Identifying Critical Features

The prototype analysis revealed several key areas requiring specific tolerance control:

• Engine mounting holes demand precise positioning for proper alignment and assembly

• Contact surfaces between components need controlled flatness for optimal seating

• Support ribs require basic dimensional control to maintain structural integrity

• Reference planes establish critical datums for measuring other features

Tolerance Class Assignment

The engineering team assigned tolerance classes based on functional requirements:

Feature	Class	Justification
Mounting Holes	Fine	Critical alignment ensures proper assembly and operation
Contact Surfaces	Medium	Balanced accuracy maintains component interface performance
Support Structure	Coarse	Basic control provides adequate strength characteristics
Main Body	Very Coarse	General dimensions maintain overall size requirements

Managing Special Cases

Beyond Standard Tolerances

ISO 2768 provides general guidelines, but certain situations demand tighter specifications:

• High-speed rotating components require precise geometric control for proper operation

• Safety-critical features need enhanced dimensional accuracy for reliable performance

• Precision mechanical interfaces demand closer tolerances than standard specifications

Title Block Requirements

Manufacturing teams must review drawing title blocks for complete tolerance information:

• Default ISO 2768 tolerance class specification guides general manufacturing

• Special tolerance requirements override standard specifications when indicated

• Project-specific modifications receive clear documentation in designated areas

• Quality control specifications define inspection requirements and acceptance criteria

Implementation Success Factors

Engineers should consider several factors when applying ISO 2768:

• Available manufacturing capabilities influence achievable tolerance ranges

• Material properties affect dimensional stability during production

• Environmental conditions impact measurement accuracy and part variation

• Production volume requirements guide economic tolerance selection

Benefits of Using ISO 2768

ISO 2768 brings significant advantages to modern manufacturing operations. Its implementation helps companies achieve better quality, lower costs, and improved efficiency. Let's explore these key benefits.

Interchangeability of Parts

Parts made in different factories must fit together perfectly. ISO 2768 makes this possible by setting clear rules for size differences. When manufacturers follow these rules:

• Parts from various suppliers fit together without needing extra adjustments

• Assembly lines run smoothly because components match consistently every time

• Replacement parts work correctly when old parts need changing

Design Consistency

Engineers worldwide speak the same language through ISO 2768. This common understanding helps:

• Design teams create clear drawings everyone understands

• New team members quickly learn standard tolerance practices

• Different departments work together more effectively

Think of it like a recipe book - when everyone uses the same measurements, the results stay consistent.

Quality Control

ISO 2768 makes checking part quality easier and more reliable. Quality teams benefit from:

Aspect	Improvement
Inspection	Clear pass/fail criteria for measurements
Documentation	Standard formats for recording quality data
Training	Simplified instruction for quality staff
Consistency	Same quality standards across all shifts

Cost Reduction

Smart use of ISO 2768 saves money in many ways:

• Manufacturing becomes faster by reducing unnecessary precision requirements

• Less waste occurs because tolerance requirements match real needs

• Fewer parts get rejected during inspection processes

• Training costs decrease through standardized procedures

International Compatibility

Business becomes easier across borders. ISO 2768 helps by:

• Creating trust between international business partners

• Reducing confusion when working with overseas suppliers

• Making it simpler to sell products in different countries

• Supporting global manufacturing operations

Real-World Impact

Companies using ISO 2768 see practical benefits:

• Production speeds increase because everyone understands the requirements

• Parts fit right the first time, reducing assembly problems

• Customer satisfaction improves through consistent quality

• Business grows easier across international markets

Making It Work

To get these benefits, companies should:

• Train their teams on ISO 2768 standards

• Update their technical drawings to include proper tolerances

• Use the right tools for measuring parts

• Keep good records of quality checks

These simple steps help businesses make better products while saving time and money. ISO 2768 might seem complex at first, but its benefits make it worth learning and using.

Other Certifications and Accreditations Similar to ISO 2768

Manufacturing excellence requires compliance with various international standards. While ISO 2768 focuses on dimensional tolerances, other certifications ensure broader aspects of quality, safety, and efficiency.

ISO 9001: Quality Management Systems

ISO 9001 establishes comprehensive quality management requirements across industries. This certification:

• Demonstrates organizational commitment to consistent product and service quality

• Enhances customer satisfaction through systematic process improvements

• Streamlines documentation and internal communication procedures

• Supports continuous improvement in operational efficiency

ISO 14001: Environmental Management

Modern manufacturing must consider environmental impact. ISO 14001 provides:

Focus Area	Benefits
Resource Management	Optimized material usage and waste reduction
Environmental Impact	Reduced pollution and improved sustainability
Legal Compliance	Assured adherence to environmental regulations
Corporate Image	Enhanced reputation for environmental responsibility

ISO/IEC 17025: Laboratory Excellence

Testing facilities require specific standards. ISO/IEC 17025 addresses:

• Precise calibration procedures ensuring measurement accuracy across testing equipment

• Standardized testing methodologies producing reliable, repeatable results

• Comprehensive documentation systems tracking all laboratory activities

• Professional competency requirements for laboratory personnel

AS9100: Aerospace Specifications

Aerospace manufacturing demands exceptional precision. AS9100 builds upon ISO 9001 by adding:

• Rigorous control systems for aviation, space, and defense components

• Enhanced traceability requirements throughout production processes

• Strict risk management protocols ensuring product safety

• Specialized supplier management guidelines for aerospace applications

ISO/TS 16949: Automotive Standards

Automotive production requires unique considerations. This standard ensures:

• Consistent quality across global automotive supply chains

• Defect prevention through robust quality planning

• Reduction in variation and waste in automotive components

• Continuous improvement in manufacturing processes

ISO 13485: Medical Device Manufacturing

Healthcare products demand extraordinary care. ISO 13485 provides:

Requirement	Purpose
Risk Management	Patient safety assurance throughout product lifecycle
Process Control	Consistent production of safe medical devices
Documentation	Complete traceability of all manufacturing processes
Regulatory Compliance	Adherence to medical device regulations

Summary

ISO 2768 plays a crucial role in ensuring precision across various industries. Its use simplifies the design process and provides clarity in manufacturing specifications. By adopting ISO 2768 in technical drawings, designers and manufacturers can streamline production, reduce errors, and enhance global collaboration.

Using this standard helps minimize miscommunication, increases part interchangeability, and improves quality control. Whether you're in CNC machining, aerospace, or industrial design, applying ISO 2768 ensures both cost-effectiveness and precision in part manufacturing.