General Tolerance Iso 2768-mk May 2026

| Shorter side length range | Tolerance (mm) | |----------------------------|----------------| | ≤ 100 | 0.2 | | >100 – 300 | 0.3 | | >300 – 1000 | 0.4 | | >1000 – 3000 | 0.5 |

ISO 2768-mk represents the gold standard for general tolerances in modern mechanical engineering. It harmoniously blends the 'medium' linear tolerances with 'medium' geometric controls to produce parts that are both functional and economical.

For the designer, using 'mk' cleans up drawings and signals a mature understanding of manufacturing realities. For the machinist, it provides clear, enforceable limits for size and geometry. For the quality engineer, it defines the precise inspection criteria.

Final Rule of Thumb: Use ISO 2768-mk for the majority of machined, cast, or 3D-printed metal parts where features assemble without extreme precision. Save specific tolerances only for critical interfaces. This practice will elevate your engineering drawings from ambiguous sketches to professional, internationally compliant manufacturing instructions.

This report outlines the application and specifications of the ISO 2768-mK general tolerance standard, which is widely used in mechanical engineering to simplify technical drawings by providing standard tolerances for dimensions and geometric features that do not have individual callouts. 1. Scope and Application

ISO 2768-mK is an international standard that defines general tolerances for machining processes, such as CNC machining. It is typically indicated in the drawing's title block as "General Tolerance: ISO 2768-mK".

ISO 2768-1 (m): Represents the "medium" tolerance class for linear and angular dimensions (external sizes, diameters, radii, distances).

ISO 2768-2 (K): Specifies general geometric tolerances, primarily for flatness, straightness, parallelism, and symmetry. 2. Tolerance Class "m" (Linear & Angular)

The "m" (medium) class is the most common choice for metal parts. It sets permissible deviations based on the nominal size of the dimension: Nominal Size (mm) Tolerance (± mm) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 4000 0.5 to 2.0 (variable) Data sourced from LEADRP and ZEISS Quality Forum. 3. Tolerance Class "K" (Geometric)

The "K" class defines general limits for the form and position of features. For example, surfaces with fitting dimensions must remain flat and parallel within the specified K-class range to ensure assembly functionality. 4. Technical Advantages

Simplification: Reduces drawing complexity by eliminating the need to label every single dimension with a specific tolerance.

Cost Efficiency: Using a standard "medium" tolerance helps avoid unnecessarily tight specifications that drive up manufacturing costs.

Consistency: Provides a baseline for quality inspection across different suppliers and manufacturing facilities. General Tolerance - ISO 2768 1 & 2 - ZEISS Quality Forum

To apply the standard correctly, engineers and machinists must refer to the exact numeric values.

ISO 2768-mk provides a cost-effective, industry-standard default tolerance for machined parts where precision is not critical. It balances manufacturing ease with acceptable quality. However, engineers must explicitly specify tighter tolerances for mating, safety, or high-precision features. This report shall be appended to the company’s quality management system (QMS) as the reference for general tolerance compliance.

Approved by:

[Name], Lead Engineer
Date: ___________

The Ultimate Guide to ISO 2768-mK: Streamlining Your Manufacturing Drawings

In the world of precision engineering and CNC machining, time is money—and clarity is king. If you’ve ever looked at a technical drawing and seen "ISO 2768-mK" in the title block, you’re looking at one of the most powerful tools for simplifying design and communication. general tolerance iso 2768-mk

But what exactly does it mean, and why is it the industry standard? Let’s break it down. What is ISO 2768-mK?

ISO 2768-mK is an international standard that provides a simplified system of general tolerances for linear and geometrical dimensions. Instead of manually labeling every single dimension on a complex drawing, engineers use this shorthand to define acceptable levels of precision for all non-critical features.

The notation "mK" combines two distinct parts of the standard:

"m" (Medium): Refers to ISO 2768-1, which governs linear and angular dimensions (like lengths, radii, and diameters).

"K" (Medium Geometrical): Refers to ISO 2768-2, which controls geometrical deviations such as straightness, flatness, and perpendicularity. Why "Medium" (mK) is the Industry Favorite

While there are other classes—such as "f" (fine) for high precision or "c" (coarse) for loose fits—the mK combination is the most widely used, representing about 80% of typical manufacturing requirements.

Cost Efficiency: Tighter tolerances (like ISO 2768-f) can be 2 to 2.5 times harder and more expensive to machine. The "mK" class offers a sweet spot between precision and production speed.

Reduced Complexity: It prevents drawings from becoming cluttered with hundreds of individual tolerance notes, making them much easier to read.

Global Language: Because it's an international standard, a part designed with ISO 2768-mK in Germany can be manufactured in Australia or the US with zero ambiguity. Breaking Down the Tables

To use the standard effectively, you need to know how the nominal size of a feature dictates its allowable deviation. Here is a look at the "m" and "K" standards: Linear Dimensions (ISO 2768-m)

For standard linear measurements like length or diameter, the permissible deviation increases as the part gets larger. Nominal Length Range (mm) Tolerance (± mm) 120 to 400 Source: Derived from General Tolerances ISO 2768-1 Geometrical Tolerances (ISO 2768-K)

This part controls the "form" of the part. For example, "K" ensures a surface stays reasonably flat or straight without needing a specific GD&T callout for every face. The General CNC Machining Tolerance: ISO 2768-mk

ISO 2768-mK is an international standard for general tolerances used to simplify technical drawings by providing default limits for dimensions and geometric features that do not have specific tolerance markers. 🛠️ What "mK" Means

The designation combines two different parts of the standard:

m (Part 1): Represents the Medium tolerance class for linear and angular dimensions (lengths, radii, angles).

K (Part 2): Represents the K tolerance class for geometrical features (flatness, straightness, perpendicularity, symmetry). ISO 2768-1: Linear Dimensions (Class m)

These tolerances apply to dimensions like length, width, and diameter when not specified. All values below are in mm. Nominal Range (mm) Tolerance (±) 120 to 400 400 to 1000 1000 to 2000 2000 to 4000 Additional "m" class values:

External Radii & Chamfers: ±0.2 mm (for 0.5–3mm) to ±1.0 mm (over 30mm). | Shorter side length range | Tolerance (mm)

Angular Dimensions: ±1° (up to 10mm length) to ±0°10' (over 400mm). ISO 2768-2: Geometrical Tolerances (Class K)

This part controls the shape and position of features to ensure they fit correctly. Feature Type Tolerance Rule for Class K Straightness / Flatness

Ranges from 0.05 mm (up to 10mm length) to 0.6 mm (over 1000mm). Perpendicularity Max 0.6 mm for lengths up to 300mm. Symmetry Max 0.6 mm up to 300mm length. Run-out 0.2 mm (standard for class K). 🎯 When to Use ISO 2768-mK Understanding ISO 2768-mK Tolerances for Engineers

ISO 2768-mK standard defines general tolerances for dimensions and geometric features on technical drawings where specific tolerances are not indicated. It simplifies drawings by providing a default "medium" level of precision, ensuring parts fit together without over-specifying every dimension. Meaning of "mK" "m" (Medium) : Refers to ISO 2768-1 , covering general tolerances for linear and angular dimensions (lengths, diameters, radii, chamfers). "K" (Medium) : Refers to ISO 2768-2 , covering general geometrical tolerances

(straightness, flatness, perpendicularity, symmetry, and circular run-out). Tolerance Tables for ISO 2768-mK All values are in millimeters (mm) unless otherwise stated. ALFA MIMtech 1. Linear Dimensions (Class m) Applies to external sizes, internal sizes, and diameters. Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm >6 to 30 mm >30 to 120 mm >120 to 400 mm >400 to 1000 mm >1000 to 2000 mm >2000 to 4000 mm 2. External Radii and Chamfer Heights (Class m) Applies to broken edges and rounded corners. ALFA MIMtech Range (Nominal Size) Tolerance (±) 0.5 to 3 mm >3 to 6 mm 3. Angular Dimensions (Class m) Applies to angular measurements. ALFA MIMtech Length of Short Side Tolerance (±) Up to 10 mm >10 to 50 mm >50 to 120 mm >120 to 400 mm Over 400 mm 4. Geometrical Tolerances (Class K) Applies to the form and position of features. waterson.com Feature Type Range (Nominal Length) Straightness & Flatness Up to 10 / 30 / 100 / 300 / 1000 / 3000 mm 0.05 / 0.1 / 0.2 / 0.4 / 0.6 / 0.8 mm Perpendicularity Up to 100 / 300 / 1000 / 3000 mm 0.4 / 0.6 / 0.8 / 1.0 mm Up to 100 / 300 / 1000 / 3000 mm 0.6 / 0.6 / 0.8 / 1.0 mm Circular Run-out All lengths Important Considerations Understanding ISO 2768-mK Tolerances for Engineers

Understanding General Tolerance ISO 2768-mk In the world of precision manufacturing, specifying a tolerance for every single dimension on a technical drawing is both time-consuming and prone to error. ISO 2768 is an international standard designed to solve this by providing "general tolerances" that act as a default for any dimension without an individual specification.

The callout ISO 2768-mk is the most common general tolerance designation used globally, particularly for CNC machining and sheet metal fabrication. It combines two distinct parts of the standard to cover both physical size and geometric form. 1. What does "mk" stand for?

The designation consists of two lowercase and uppercase letters, each representing a specific tolerance class from a different part of the ISO 2768 standard:

m (Medium): Refers to ISO 2768-1. This lowercase letter defines the permissible deviations for linear and angular dimensions (size).

k (Medium/Standard): Refers to ISO 2768-2. This uppercase letter defines the permissible deviations for geometrical features (form and position), such as flatness, straightness, and perpendicularity.

Together, ISO 2768-mk tells the manufacturer: "For any dimension on this drawing that doesn't have a specific tolerance next to it, use the 'Medium' dimensional class and the 'K' geometrical class." 2. ISO 2768-1: Linear and Angular Dimensions (The 'm')

This part of the standard covers lengths, diameters, radii, and angles. The "m" (medium) class is the industry's "sweet spot," balancing functional accuracy with cost-effective manufacturing. Linear Dimension Tolerances (mm)

For a nominal size (the dimension on the drawing), the permissible deviation under class m is: Nominal Size Range (mm) Tolerance (± mm) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Over 400 to 1000 Data sourced from ZEISS Quality Forum. External Radii and Chamfer Heights (mm)

For rounded edges or broken corners, the tolerances are slightly different: 0.5 to 3 mm: ±0.2 mm Over 3 to 6 mm: ±0.5 mm Over 6 mm: ±1.0 mm 3. ISO 2768-2: Geometrical Tolerances (The 'k')

While Part 1 handles size, Part 2 handles the shape of the part. The K class provides standard control over how straight, flat, or perpendicular a feature must be. Straightness and Flatness

These tolerances ensure a surface or line isn't excessively curved or warped. For class K, the limits are based on the length of the longest side: Length of Surface/Line (mm) Tolerance (mm) 100 to 300 300 to 1000 Information according to Engineers Edge. Other Geometrical Controls in Class K

Perpendicularity: Controls the 90-degree relationship between surfaces (e.g., 0.6 mm for lengths up to 300 mm).

Symmetry: Ensures features are centered correctly (e.g., 0.6 mm for lengths up to 300 mm). [Name], Lead Engineer Date: ___________ The Ultimate Guide

Circular Run-Out: Controls the variation of a surface as it rotates (standardized at 0.2 mm for class K). 4. Why Use ISO 2768-mk?

Simplified Drawings: Instead of thousands of individual ± signs, you have one note in the title block.

Global Standard: A factory in Germany (where it is often called DIN ISO 2768) and a factory in China understand the exact same limits.

Cost Efficiency: It prevents "over-tolerancing." If a non-critical bracket is made to a "Fine" (f) tolerance when "Medium" (m) would do, the price can double due to increased inspection and slower machining. 5. Critical Limitations

Engineers must remember that ISO 2768 is a general safety net, not a replacement for critical design work:

Does NOT cover threads: Thread tolerances (like 6H or 6g) must be specified separately.

Does NOT cover Fits: If you need a precision shaft to slide into a hole, you must use a standard like ISO 286 (e.g., H7/g6) instead of general tolerances.

Explicit Overrides General: If you write "±0.05" next to a dimension, that specific value overrides the general ISO 2768-mK class for that feature.

The notation ISO 2768-mk combines two different tolerance classes.

ISO 2768-mk saves you time and money. It tells your machinist: “I don’t need a micrometer for every single edge. Just machine it cleanly and consistently.”

However, it is not a magic wand. Always ask yourself: “If this dimension drifts by 0.2mm, will my assembly fail?” If the answer is yes, add a specific tolerance (e.g., 10.0 ±0.01mm) directly next to that dimension.

Use ‘mk’ for the 90% of your drawing that doesn’t matter. Use specific tolerances for the 10% that does.

Do you use ISO 2768-mk on your drawings? Have you ever had a part fail because the general tolerance was too loose? Let us know in the comments below.

Before focusing on the "mk" classification, it is essential to understand the parent standard. ISO 2768 is an international standard titled "General tolerances for linear and angular dimensions without individual tolerance indications."

It is divided into two parts:

When a drawing states "ISO 2768-mk", it is referencing both parts: the 'm' (medium) from Part 1 for linear/angular tolerances, and the 'k' (medium) from Part 2 for geometrical tolerances.

| Nominal Size Range (mm) | Tolerance ‘k’ (mm) | | :--- | :--- | | Up to 100 | 0.1 | | >100 to 300 | 0.2 | | >300 to 1000 | 0.3 | | >1000 to 3000 | 0.4 |

Note: For symmetry and runout (ISO 2768-2), the ‘k’ class generally allows 0.2mm for most common part sizes.