ISO 2768-mK is an international standard that provides "general tolerances" for manufacturing. It is primarily used to simplify technical drawings by removing the need to specify a unique tolerance for every single non-critical dimension.
When a drawing specifies "ISO 2768-mK," it combines two distinct parts of the standard to cover both size and geometric accuracy: 1. Breakdown of the "mK" Designation
"m" (Part 1): Specifies the tolerance for linear and angular dimensions. The "m" stands for the medium tolerance class, which is standard for most general engineering and machining work.
"K" (Part 2): Specifies the tolerance for geometrical features such as flatness, straightness, and perpendicularity. "K" is the middle tier of geometric classes (H, K, and L). 2. ISO 2768-1: Linear & Angular Tolerances ("m")
This part applies to external and internal sizes, diameters, radii, and distances. The permissible deviation (±) depends on the nominal length of the feature: Nominal Length (mm) Medium (m) Class (± mm) over 3 to 6 over 6 to 30 over 30 to 120 over 120 to 400 over 400 to 1000 Data source: ZEISS Quality Forum and Eurotools. 3. ISO 2768-2: Geometrical Tolerances ("K")
This section controls the "shape" of the part. If a drawing says "ISO 2768-K," the following general limits apply to features without specific geometric symbols:
Flatness & Straightness: For a length up to 100mm, the tolerance is 0.2mm.
Perpendicularity: For a length up to 100mm, the limit is 0.4mm.
Symmetry: Limits are set to ensure parts align correctly without interference. Circular Run-out: Typically set at 0.2mm for the K class. Summary of Common Use Cases
The Basics of General Tolerance Standard – ISO 2768-mK - Eurotools
The ISO 2768-mK standard is an international framework for general tolerances used in mechanical engineering to simplify technical drawings by defining default permissible deviations for dimensions and geometrical features. Instead of tolerancing every single feature, designers specify "ISO 2768-mK" in the drawing’s title block, which automatically applies a baseline level of precision to all untoleranced parts. Understanding the "mK" Designation
The designation is a combination of two distinct parts of the ISO 2768 standard:
m (lowercase): Refers to ISO 2768-1, specifically the Medium tolerance class for linear and angular dimensions.
K (uppercase): Refers to ISO 2768-2, specifically the K tolerance class for geometrical features such as flatness, straightness, and perpendicularity. ISO 2768-1: Linear and Angular Dimensions (Class m)
Part 1 defines the permissible deviations for features like lengths, diameters, radii, and angles. The "m" class is the most common for general CNC machining and sheet metal work. Nominal Length Range (mm) Tolerance Class m (± mm) over 3 to 6 over 6 to 30 over 30 to 120 over 120 to 400 over 400 to 1000 Data source: ISO 2768-2: Geometrical Tolerances (Class K)
Part 2 handles the form and orientation of features that lack specific Geometric Dimensioning and Tolerancing (GD&T) callouts. Feature Type Class K Tolerance (mm) Straightness/Flatness 0.05 to 0.8 Varies by nominal length. Perpendicularity 0.4 to 1.0 Based on the length of the shorter side. Symmetry 0.6 to 1.0 Controls uniformity across a datum plane. Circular Run-out A single value applied regardless of size. Why Use ISO 2768-mK?
Simplified Drawings: Eliminates the visual clutter of hundreds of individual tolerance notes, making prints easier to read.
Cost Efficiency: Tighter tolerances (like Class f or H) exponentially increase costs by requiring secondary finishing operations like grinding.
International Consistency: Provides a "common language" that ensures parts made in different countries—such as a design in Europe manufactured in China—will fit correctly. Common Misapplications to Avoid The General CNC Machining Tolerance: ISO 2768-mk
The ISO 2768-1 and ISO 2768-2 standards define general geometrical tolerances for parts produced by machining or metal removal. The designation "mK" indicates a specific combination of tolerance classes for linear/angular dimensions and geometrical features. Understanding the "mK" Designation Tolerance Iso 2768 Mk Pdf
m (Lower Case): Refers to ISO 2768-1, representing the "medium" tolerance class for linear and angular dimensions (e.g., lengths, radii, and diameters).
K (Upper Case): Refers to ISO 2768-2, representing the "K" tolerance class for general geometrical tolerances (e.g., flatness, straightness, and symmetry). ISO 2768-1: Linear & Angular Dimensions (Class "m")
This section covers dimensions without individual tolerance indications. All values in the table below are in millimeters (mm). Nominal Size Range (mm) 120 to 400 400 to 1000 1000 to 2000 Tolerance (m - medium) ±0.1plus or minus 0.1 ±0.1plus or minus 0.1 ±0.2plus or minus 0.2 ±0.3plus or minus 0.3 ±0.5plus or minus 0.5 ±0.8plus or minus 0.8 ±1.2plus or minus 1.2
External Radii and Chamfer Heights: For the "m" class, the tolerance is ±0.2plus or minus 0.2 mm for sizes 0.5–3 mm and ±0.5plus or minus 0.5 mm for sizes 3–6 mm.
Angular Dimensions: For the "m" class, the tolerance ranges from ±1∘plus or minus 1 raised to the composed with power (for lengths up to 10 mm) to (for lengths over 400 mm). ISO 2768-2: Geometrical Tolerances (Class "K")
This section applies to features like straightness, flatness, and perpendicularity. Nominal Length Range (mm) 100 to 300 300 to 1000 1000 to 3000 Straightness/Flatness Perpendicularity Symmetry
Run-out: The tolerance for circular run-out in class K is 0.2 mm. Why Use ISO 2768 mK?
Simplification: It removes the need to specify tolerances for every single dimension on a drawing, keeping it clean and readable.
Standardization: It ensures that a machine shop understands the required level of precision based on standard workshop capabilities.
Cost Efficiency: Using "medium" tolerances (m) is generally cost-effective as it aligns with standard CNC machining capabilities without requiring expensive precision finishing. Practical Implementation
When using this standard, the drawing title block should explicitly state: ISO 2768-mK. This informs the manufacturer that any dimension without a specific tolerance must adhere to the "medium" and "K" class values listed above.
ISO 2768-mk: The Complete Guide to General Tolerances In the world of precision manufacturing, specifying every single dimension with a dedicated tolerance would make technical drawings unreadable and engineering hours prohibitively expensive. This is where ISO 2768 comes in.
If you are looking for a Tolerance ISO 2768 mk PDF, you are likely trying to understand how to apply "General Tolerances" to your machined parts. This guide breaks down what "mk" means, how to read the tables, and why it is the industry standard for linear and geometric features. What is ISO 2768?
ISO 2768 is an international standard created to simplify drawing specifications. it establishes general tolerances for linear and angular dimensions without individual tolerance indications. The standard is divided into two parts:
Part 1 (ISO 2768-1): Focuses on linear and angular dimensions (represented by letters f, m, c, v).
Part 2 (ISO 2768-2): Focuses on geometric tolerances for features (represented by letters H, K, L).
When a drawing specifies ISO 2768-mk, it is combining "Medium" (m) from Part 1 and "Class K" (K) from Part 2. Decoding "mk": The Precision Classes
The designation "mk" consists of two distinct accuracy grades: 1. The "m" (Medium) – Linear Dimensions
Under ISO 2768-1, there are four tolerance classes for linear and angular dimensions: f (fine) m (medium) c (coarse) v (very coarse) ISO 2768-mK is an international standard that provides
The "m" class is the most common in mechanical engineering, providing a balance between functional precision and manufacturing cost. 2. The "k" (Class K) – Geometric Tolerances
Under ISO 2768-2, there are three tolerance classes for general geometrical tolerances: H (High) K (Medium) L (Low)
Class K covers general tolerances for straightness, flatness, perpendicularity, symmetry, and circular run-out. ISO 2768-1: Linear Dimensions Table (m)
For the "m" designation, the following tolerances apply based on the size of the dimension: Nominal Size (mm) Tolerance (± mm) 120 to 400 400 to 1000 1000 to 2000 ISO 2768-2: Geometrical Tolerances (K)
The "k" designation defines how much a feature can deviate geometrically. For Class K, the limits for straightness and flatness are: Nominal Length (mm) Tolerance (mm) 100 to 300 300 to 1000 Why is ISO 2768-mk Important?
Clarity: It keeps drawings clean. Engineers only need to specify tolerances for critical dimensions (like bearing fits), while "mk" handles the rest.
Cost Efficiency: By using general tolerances, machine shops know they don't need to over-process non-critical areas, which lowers the price of the part.
Universal Language: Since it is an ISO standard, a drawing made in Europe can be perfectly understood by a manufacturer in Asia or America. How to use this in your Drawings
To apply these standards, simply add a note in or near the title block of your technical drawing: General Tolerances: ISO 2768-mk
By doing this, you legally and technically define the allowable error for every dimension on that page that doesn't have a specific tolerance attached to it. Conclusion
Understanding ISO 2768-mk is essential for any hardware engineer or machinist. It ensures that parts fit together without requiring unnecessary (and expensive) precision.
If you are downloading a Tolerance ISO 2768 mk PDF, ensure you are looking at the most recent version of the ISO tables to ensure your manufacturing remains compliant with modern international standards.
The ISO 2768-mK standard is an international specification used to simplify technical drawings by providing "general tolerances" for parts manufactured by machining or metal forming. Instead of specifying a tolerance for every single dimension on a drawing, designers can simply reference "ISO 2768-mK" in the title block to cover all non-toleranced dimensions. Breakdown of "mK"
The designation consists of two parts that refer to different precision levels:
m (Medium): Refers to Part 1 of the standard, covering linear and angular dimensions (e.g., lengths, radii, and angles).
K (Geometric): Refers to Part 2 of the standard, covering geometrical characteristics such as straightness, flatness, and perpendicularity. ISO 2768-1: Linear & Angular (Class m)
This section defines the permissible deviations for dimensions like lengths, diameters, and external radii. The "m" (medium) class is the most common for standard industrial machining. Table 1: Linear Dimensions (Permissible deviations in mm) Nominal Range (mm) Class f (fine) Class m (medium) Class c (coarse) ±0.05plus or minus 0.05 ±0.1plus or minus 0.1 ±0.2plus or minus 0.2 Over 3 to 6 ±0.05plus or minus 0.05 ±0.1plus or minus 0.1 ±0.3plus or minus 0.3 Over 6 to 30 ±0.1plus or minus 0.1 ±0.2plus or minus 0.2 ±0.5plus or minus 0.5 Over 30 to 120 ±0.15plus or minus 0.15 ±0.3plus or minus 0.3 ±0.8plus or minus 0.8 Over 120 to 400 ±0.2plus or minus 0.2 ±0.5plus or minus 0.5 ±1.2plus or minus 1.2 Over 400 to 1000 ±0.3plus or minus 0.3 ±0.8plus or minus 0.8 ±2.0plus or minus 2.0 ISO 2768-2: Geometrical Tolerances (Class K)
This part limits how much a feature can deviate in shape or orientation. Class K is the intermediate level between H (tightest) and L (loosest). Key Geometric Controls (Class K) Straightness and Flatness: Ranges from for small parts up to for lengths over Perpendicularity: Maximum deviation of depending on the length of the shorter leg. Symmetry: Standardized at for class K. Circular Run-out: Fixed at for class K. Core Benefits
Cleaner Drawings: Eliminates "dimension clutter" by removing repetitive ±plus or minus The "One Line" Rule for Drawings To apply
Cost Efficiency: Avoids unnecessarily tight tolerances that drive up manufacturing costs.
Manufacturing Readiness: Provides a clear baseline that matches standard workshop capabilities.
📍 Application Note: If a specific feature requires higher precision (e.g., a bearing fit), that specific dimension must be toleranced individually, which then overrides the general ISO 2768 standard.
For full technical charts, you can reference the ISO 2768-mK Overview or specialized guides from ZEISS Quality Forum.
If you tell me the material or manufacturing process you're using (e.g., CNC milling vs. sheet metal), I can help you decide if class mK is the right choice for your project.
| Dimension Type | Applies To | |---------------|-------------| | Linear dimensions (mm) | Lengths, widths, heights, diameters, radii, chamfers | | Angular dimensions (°/') | Angles, unless otherwise specified | | Geometric tolerances | Straightness, flatness, circularity, cylindricity, parallelism, perpendicularity, symmetry, runout |
To apply this standard, add a note in the title block of your engineering drawing:
"GENERAL TOLERANCES ISO 2768-mK"
This single line replaces dozens of individual tolerance boxes, cleans up the drawing, and clearly defines the acceptable limits for the manufacturer.
Conclusion: ISO 2768-mK is the "Goldilocks" of machining tolerances—not too tight (expensive), not too loose (non-functional). It is perfect for 80% of standard mechanical parts.
Disclaimer: This article is for informational purposes. Always verify tolerances against the official ISO 2768:1989 standard for your specific application.
The "m" class (Medium) is the default assumption for most machining operations using standard workshop equipment. It represents a balance between precision and manufacturability.
| Do NOT use ISO 2768-mK for ... | Reason | |--------------------------------|--------| | Press fits, bearing seats, sliding fits | Needs explicit tolerances (e.g., ISO 286) | | Thread dimensions | Follow thread standards (e.g., ISO 965) | | Welded assemblies | Welding shrinkage invalidates general tolerances | | Plastic or rubber parts | Material flexibility requires tighter/looser control | | High-precision medical, aerospace, or optics | Risk of functional failure |
While this article provides a summary, engineers should always refer to the official standard for legal and contractual compliance. You cannot get the copyrighted PDF for free legally, but you can purchase or view it via:
Searching for a free "ISO 2768 MK PDF" is dangerous. Many "free" versions online are:
Where to get the legitimate PDF:
| Nominal Dimension Range | Tolerance for "m" (Medium) | | :--- | :--- | | 0.5 mm up to 3 mm | ± 0.1 mm | | > 3 mm up to 6 mm | ± 0.1 mm | | > 6 mm up to 30 mm | ± 0.2 mm | | > 30 mm up to 120 mm | ± 0.3 mm | | > 120 mm up to 400 mm | ± 0.5 mm | | > 400 mm up to 1000 mm | ± 0.8 mm | | > 1000 mm up to 2000 mm | ± 1.2 mm |
Practical Example: If a shaft length is drawn as 100 mm without an individual tolerance, under ISO 2768-mK, it can be between 99.7 mm and 100.3 mm.
In the world of mechanical engineering and manufacturing, drawings are the language of communication. However, if every single dimension on a drawing had to be accompanied by a specific tolerance (e.g., $25.00 \pm 0.05$), technical drawings would become cluttered, difficult to read, and expensive to produce.
This is where ISO 2768 comes into play. This international standard defines general tolerances for linear and angular dimensions. Specifically, the designation ISO 2768-mK is one of the most common specifications found on mechanical drawings today.
This article explores what ISO 2768-mK means, how to interpret its tables, and why it is essential for cost-effective manufacturing.