ISO 2768 is the international standard for general tolerances used in technical drawings. It simplifies the design process by providing default values for dimensions without specific tolerance callouts. What is ISO 2768?
Engineers use ISO 2768 to define the allowable deviation for linear and angular dimensions. Without general tolerances, every single dimension on a blueprint would require an individual ± value. This would make drawings cluttered and difficult to read. By referencing "ISO 2768" in the title block, a manufacturer knows exactly how much "wiggle room" they have for non-critical features. Part 1: ISO 2768-1 (Linear and Angular Dimensions)
This part focuses on the "size" of features. It is divided into four tolerance classes, ranging from very precise to coarse. Tolerance Classes
f (Fine): Used for precision machining and high-end components.
m (Medium): The most common standard for general engineering. c (Coarse): Used for rough parts or non-mating surfaces.
v (Very Coarse): Used for structural components where fit is not critical. Table 1: Linear Dimensions (mm) Nominal Size (mm) m (Medium) c (Coarse) v (Very Coarse) 120 to 400 Part 2: ISO 2768-2 (Geometrical Tolerances)
While Part 1 handles length and width, Part 2 handles the "shape" and "orientation" of a part. It uses three tolerance classes: H, K, and L. Geometric Characteristics Covered:
🚀 Straightness and Flatness: Ensures surfaces are truly level.
📐 Perpendicularity: Controls the 90-degree angle between surfaces. 🎯 Symmetry: Ensures features are centered correctly. 🔄 Circular Run-out: Limits wobbling in rotating parts. Table 2: Flatness and Straightness (mm) Range (mm) 100 to 300 Why Use an ISO 2768 PDF?
Having a PDF version of these tables is essential for several reasons:
Consistency: Ensures that the machine shop and the design office are looking at the same data.
Speed: Designers can quickly check if a standard "medium" tolerance fits their assembly needs.
Cost Reduction: Specifying "Medium" instead of "Fine" where precision isn't needed saves significant manufacturing time and money. How to indicate it on a drawing Look for a note in the title block that looks like this: ISO 2768-mK The "m" refers to the linear tolerance class (Medium). The "K" refers to the geometric tolerance class. Summary Checklist for Designers
✅ Check your fit: Does the "m" class provide enough clearance for moving parts? Iso 2768 General Tolerances Pdf
✅ Title Block: Ensure the ISO 2768 standard is explicitly mentioned.
✅ Critical Dimensions: If a dimension is vital for safety or function, do not rely on ISO 2768. Give it a specific tolerance (e.g., 20.00 +0.02/-0.00). If you'd like to dive deeper, I can help you with:
Determining which tolerance class (f, m, c, v) is best for your specific project.
Explaining how ISO 2768 compares to ISO 286 (Hole/Shaft fits).
Finding specific tolerance values for very large dimensions (over 1000mm). 5?
In the heart of the Swiss Alps, inside a high-tech workshop carved into granite, a master watchmaker named Elias faced a crisis. He wasn't building a watch; he was building the "Aeon Key," a device designed to synchronize the world's atomic clocks.
His apprentice, Leo, hurried in with a stack of blueprints. "The casing arrived from the machinist, Elias, but the interlocking gears won't budge. They’re stuck."
Elias didn't look up from his loupe. "Did you specify the tolerances, Leo?"
Leo hesitated. "I sent the PDF. I told them to follow ISO 2768."
Elias finally looked up, his eyes sharp. "ISO 2768 is a language, Leo, not just a label. It’s the silent agreement between the designer’s dream and the machine’s reality. If you don't understand the 'General Tolerances,' you're building a puzzle with pieces from two different worlds." The Rule of the "General"
Elias pulled up the ISO 2768-1 table on a screen. "Look here," he pointed to the classes: f (fine), m (medium), c (coarse), and v (very coarse).
"Most people think a PDF is just a document," Elias explained. "But in engineering, ISO 2768 is the 'safety net.' It defines how much a part can stray from its 'perfect' dimension when no specific tolerance is written next to a measurement. It simplifies drawings so they don't look like a swarm of bees." The Medium Mistake
Leo looked at the blueprint. In the title block, it simply read: ISO 2768-m. ISO 2768 is the international standard for general
"You chose 'm' for Medium," Elias noted. "For a length between 30mm and 120mm, that gives the machinist a deviation of . In the world of high-precision synchronization,
is a canyon. The gears are seizing because your 'General Tolerance' was too generous." Geometry of Silence
He then flipped to ISO 2768-2, which covers Geometrical Tolerances—things like flatness, symmetry, and circular run-out.
"Even if the size is right, is the part straight? Is it round? Class K or H would have saved us. Because you left it to the 'General' standard without picking the right class, the machinist followed the law, but the machine failed the mission." The Lesson Learned
Leo took the tablet, adjusted the title block to ISO 2768-fH (Fine for linear, High for geometry), and sent the revised PDF back to the shop.
Weeks later, the Aeon Key hummed to life. The gears didn't just fit; they glided. Leo realized then that ISO 2768 wasn't just a PDF in a folder—it was the invisible boundary where human imagination meets the hard limits of metal.
The ISO 2768 standard is a foundational document in mechanical engineering, providing a global language for general tolerances
on technical drawings. By referencing this standard, engineers can avoid the tedious and cluttering task of specifying individual tolerances for every single dimension, relying instead on a set of "default" accuracy levels. Why ISO 2768 is Essential
In modern manufacturing, every feature on a part has a theoretical size and shape, but real-world processes like CNC machining or sheet metal forming always involve slight deviations. ISO 2768 ensures that: Standard Tolerances in Manufacturing: ISO 2768 & ISO 286
ISO 2768 is a foundational international standard used to simplify engineering drawings by defining general tolerances
for dimensions that don't have specific values listed next to them
. It is widely considered an industry essential for machining and sheet metal work. ISO - International Organization for Standardization Overview of ISO 2768 The standard is split into two critical parts: ISO 2768-1 linear and angular dimensions (e.g., lengths, diameters, radii, and chamfer heights). ISO 2768-2 geometrical tolerances
(e.g., straightness, flatness, perpendicularity, and symmetry). Precision Levels (Tolerance Classes) ISO 2768 provides convenience but can obscure functional
Designers typically select a class based on the manufacturing process's capability: Part 1 Classes (coarse), and (very coarse). Part 2 Classes (often paired with Part 1, e.g., "ISO 2768-mK"). Review: Why Pros Use It Experts from highlight several benefits and a few critical cautions: Efficiency
: It saves massive amounts of design time. Instead of tolerancing 100 individual dimensions, you simply note "ISO 2768-m" in the title block to cover non-critical features. Cost Reduction
: By using "medium" or "coarse" classes for non-functional areas, you avoid over-specifying, which keeps machining costs down. Global Language
: It ensures your drawings are interpreted the same way in a local shop as they would be in a factory halfway across the world. Caveat - Tolerance Stacking
: A common critique is that relying solely on general tolerances can lead to "stacking" issues, where multiple variations add up and prevent a final assembly from fitting correctly. Caveat - Precision Limits
: For critical fits like bearings or shafts, professionals recommend using more specific standards like alongside ISO 2768. Xometry Pro Accessing the Standard
What is ISO 2768? | CNC Machining Tolerance Standards - Fictiv
| Class | Description | Typical Application | | :--- | :--- | :--- | | f | Fine | Precision engineering, small electronic components. | | m | Medium | General machinery, standard CNC parts. (Most common) | | c | Coarse | Fabricated parts, welded assemblies, castings. | | v | Very Coarse | Rough structural components, sheet metal work. |
In the title block or general notes:
"General tolerances ISO 2768-mK"
Other combos: -fH, -cL, -vK, etc.
| Nominal Size Range | Class f (Fine) | Class m (Medium) | Class c (Coarse) | Class 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 |
Note: For nominal sizes below 0.5 mm, the deviations shall be indicated directly next to the nominal dimension.