ISO 2768 General Tolerances: Tables & Tips

Almost every technical drawing for mechanical components contains the notation "ISO 2768-mK" or "General tolerance DIN ISO 2768-m" somewhere in the title block. For procurement professionals sourcing parts internationally, this is more than a reference code. It determines the dimensional deviations a manufacturer must hold — and ultimately, whether the part fits or doesn't.

In brief: ISO 2768 defines general tolerances for all dimensions not individually toleranced on a drawing. Part 1 establishes four classes for linear and angular dimensions (f, m, c, v), Part 2 three classes for form and position (H, K, L). The most common designation in mechanical engineering is ISO 2768-mK — medium accuracy for both dimensions and geometry. The standard is currently under revision — the FDIS draft has been in ballot since April 2026, with publication expected late 2026.

What Is ISO 2768 and Why Do Procurement Managers Need It?

ISO 2768 ranks among the most widely applied standards in mechanical engineering. Published by the International Organization for Standardization (ISO), it governs the permissible deviations for all dimensions on a drawing that carry no individual tolerance. Without it, every single dimension would need its own tolerance callout — an enormous effort for complex parts with 50 or more dimensions.

In international procurement, ISO 2768 serves as a silent quality anchor. Many rejections don't stem from poor manufacturing. They arise because buyer and supplier hold different assumptions about allowable deviations. The standard creates a shared language.

The standard is divided into two parts:

• ISO 2768-1: General tolerances for linear and angular dimensions

• ISO 2768-2: General tolerances for form and position (geometrical tolerances)

In Germany, the standard is published as DIN ISO 2768. It replaced the older DIN 7168, which still appears on legacy drawings. Those looking for more background on quality control in product development will find complementary fundamentals there.

What Tolerance Classes Does ISO 2768-1 Define?

Part 1 of the standard establishes four tolerance classes with different levels of manufacturing precision. Class "m" (medium) is the most prevalent — it appears on the majority of mechanical engineering drawings. Choosing the right class affects both cost and functional reliability of a component.

Why does class selection matter so much? A class that's too tight — say "f" instead of "m" — drives up manufacturing cost without functional necessity. A class that's too wide — "c" instead of "m" — can cause assembly and fit issues. The trade-off between cost and quality is decided right here.

Tolerance Table ISO 2768-1: What Deviations Are Allowed for Linear Dimensions?

The permissible limit deviations depend on the nominal dimension range. The table below shows values for all four tolerance classes in millimetres — this is the central reference for anyone working with ISO 2768.

Practical example: A non-toleranced dimension of 50 mm falls in the range "over 30 to 120". With tolerance class "m", the permissible deviation is ± 0.3 mm — the part may measure between 49.7 mm and 50.3 mm.

From our procurement experience, the range "over 120 to 400 mm" consistently generates the most discussion. Here, the difference between class f (± 0.2 mm) and class c (± 1.2 mm) reaches a factor of 6. For components in this size range, it pays to align the tolerance class deliberately with the design engineer.

Tolerance Table ISO 2768-1: What Deviations Apply to Angular Dimensions?

Beyond linear dimensions, the standard also defines limit deviations for angles. The permissible deviation depends on the shorter side of the angle — not on the angle value itself. The shorter the side, the larger the allowed deviation, because smaller geometries are harder to control in manufacturing.

Notice something? Classes "f" and "m" have identical values for angular dimensions. This means tolerance class "m" carries no penalty compared to "f" when it comes to angles — an aspect designers should factor into their class selection.

What Does ISO 2768-2 Cover for Form and Position Tolerances?

Part 2 supplements dimensional tolerances with geometrical requirements. It defines three tolerance classes (H, K, L) for characteristics like straightness, flatness, perpendicularity, symmetry, and circular run-out. Class K is considered the standard and appears in the common combination "ISO 2768-mK" on most mechanical engineering drawings.

Flatness and Straightness per ISO 2768-2

Perpendicularity per ISO 2768-2

Symmetry per ISO 2768-2

Have you noticed that symmetry tolerances for class H remain constant at 0.5 mm across all dimension ranges? That's because symmetry is inherently difficult to control in manufacturing, and even the tightest class requires a practical lower bound.

How Do You Read the Notation "ISO 2768-mK"?

The combined standard notation on a technical drawing always follows the pattern ISO 2768 – [lowercase letter][uppercase letter]. The lowercase letter (f, m, c, v) refers to Part 1 and defines the tolerance class for linear and angular dimensions. The uppercase letter (H, K, L) refers to Part 2 and sets the class for form and position tolerances.

The most common combination in general mechanical engineering is ISO 2768-mK. When only Part 1 applies, the drawing reads "ISO 2768-m" without an uppercase letter. The notation "ISO 2768-mH" appears when standard dimensional tolerances need to be combined with tighter geometrical requirements.

In our drawing review practice for international procurement projects, we occasionally see "ISO 2768-mK" on drawings that simultaneously call out individual tolerances of ± 0.02 mm at several locations. This isn't a contradiction — individual tolerances always take precedence. But it signals that the designer expects the remaining dimensions to follow a defined accuracy level as well.

When Do General Tolerances per ISO 2768 Apply?

General tolerances apply exclusively to dimensions that carry no individual tolerance on the technical drawing. As soon as a dimension is explicitly toleranced — for example 50 ± 0.05 mm — the individual tolerance takes precedence. Without a standard reference in the title block, non-toleranced dimensions are formally undefined.

That sounds straightforward, but it leads to misunderstandings in practice. Four points deserve particular attention:

• The standard applies only when explicitly referenced in the title block

• It covers dimensions produced by machining or comparable processes

• Raw castings are governed by separate standards such as ISO 8062

• Dimensions created by bending or forming are not automatically covered by ISO 2768

Those interested in a deeper look at acceptance testing and inspection certificates will find complementary information on documentation and acceptance procedures.

How Should Procurement Professionals Apply ISO 2768 in Sourcing?

For procurement managers sourcing mechanical components internationally, ISO 2768 goes far beyond a standard notation — it's a risk mitigation tool. A 2024 study by Politecnico di Milano found that targeted tolerance optimization saves 10–21% of manufacturing costs. At the same time, over-specified tolerances can increase costs by a factor of 2 to 24. Three aspects are particularly relevant.

Verify the Tolerance Class

Does the specified tolerance class match the actual functional requirements? A class that's too tight — "f" instead of "m" — inflates manufacturing cost without functional necessity. Conversely, a class that's too wide — "c" instead of "m" — can cause fit problems during assembly.

Tip: Consult your design engineer if you're unsure about class selection. Often, shifting one level up or down saves significant money — or prevents scrap.

Ensure Supplier Understanding

Not all international manufacturing partners interpret ISO 2768 identically. We recommend including the relevant tolerance tables as part of the purchase order specification — not just the standard reference. This is especially important when sourcing from Asia. Those who structure their procurement process systematically can integrate such requirements into supplier qualification.

Adapt Incoming Inspection

Inspection planning should identify dimensions that fall under general tolerances but are functionally relevant. These dimensions warrant checking at goods receipt, even if they're not individually toleranced. An AQL-based inspection method offers a proven methodology here.

Frequently Asked Questions

What does general tolerance ISO 2768-mK mean?

The notation "ISO 2768-mK" on a technical drawing means all non-individually toleranced dimensions are subject to tolerance class "m" (medium) per ISO 2768-1. Simultaneously, geometrical characteristics like flatness and perpendicularity follow class "K" per ISO 2768-2. This combination is the standard in general mechanical engineering.

Which dimensions does the general tolerance DIN ISO 2768-m cover?

The general tolerance per DIN ISO 2768-m applies to all linear and angular dimensions that carry no individual tolerance on the drawing. It does not apply to explicitly toleranced dimensions or to raw parts such as castings or forgings. The prerequisite is that the standard is referenced in the title block of the drawing.

When does the general tolerance apply?

The general tolerance per ISO 2768 applies only when the standard is explicitly referenced in the title block of the technical drawing. Without this reference, non-toleranced dimensions are formally undefined. The standard also covers only dimensions produced by machining or comparable processes — not raw parts or bent dimensions.

What does "mK" mean in general tolerances?

The lowercase "m" designates tolerance class "medium" for linear and angular dimensions (defined in ISO 2768-1). The uppercase "K" designates the medium class for form and position tolerances (defined in ISO 2768-2). Together, they form the standard combination found on the majority of mechanical engineering drawings.

What is the difference between DIN 7168 and ISO 2768?

DIN 7168 was the German predecessor standard for general tolerances. It was replaced by DIN ISO 2768 and has been withdrawn since 1991. The tolerance values were largely comparable, but class designations and structure differ. Current drawings should reference ISO 2768 exclusively. Legacy drawings with DIN 7168 references should be updated during revision.

Conclusion: Specifying Tolerances Correctly Saves Cost and Complaints

ISO 2768 is a daily working tool — for designers, quality managers, and procurement professionals alike. Understanding and correctly applying the standard in purchase specifications prevents supply chain misunderstandings, reduces scrap, and secures the functionality of your components. The tolerance tables in this article serve as a day-to-day reference.

Line Up supports you in the procurement of mechanical components with the necessary technical expertise. From drawing review to supplier qualification to incoming inspection — we ensure your tolerances are met not just on paper. Get in touch for a no-obligation consultation.