Every manufactured part exists somewhere on a spectrum between theoretical perfection and real-world variation. The question engineers must answer — repeatedly, on every drawing — is: how much variation is acceptable? Specifying individual tolerances for every dimension on a complex part can be time-consuming, prone to inconsistency, and difficult to manage across a supply chain. This is precisely the problem that ISO 2768 general tolerances were designed to solve.

ISO 2768 is an internationally recognized standard that establishes default tolerance values for linear dimensions, angular dimensions, and geometric characteristics on technical drawings. Rather than calling out a tolerance on every single feature, designers can apply a single ISO 2768 tolerance class to the entire drawing — covering all untoleranced features in one concise notation. The result is cleaner drawings, clearer communication with manufacturers, and a systematic approach to dimensional control that works across industries and processes.

This guide explains exactly how ISO 2768 is structured, what each tolerance class means in practice, when to apply the standard versus specify individual tolerances, and how to correctly call it out on your technical drawings. Whether you are working on a CNC machined component, a sheet metal enclosure, or a molded plastic housing, understanding ISO 2768 will help you design smarter and communicate more effectively with your manufacturing partner.

What Is ISO 2768?

ISO 2768 is a standard published by the International Organization for Standardization (ISO) that defines general tolerances for linear and angular dimensions, as well as geometric tolerances, on technical drawings. Its purpose is to simplify drawing annotations by allowing engineers to specify a single tolerance class that applies to all dimensions not individually toleranced. Instead of annotating every radius, chamfer, length, and angle with its own ± value, you reference ISO 2768 in the drawing title block and let the standard define the acceptable variation for all remaining features.

The standard was developed to create a common language between designers and manufacturers — particularly relevant when working with international suppliers or across different engineering teams. When a drawing notes "ISO 2768-m," any qualified manufacturer worldwide understands the implied tolerances for every unannotated dimension. This consistency reduces the risk of misinterpretation, simplifies procurement, and helps ensure that manufactured parts meet design intent without over-engineering the documentation process.

It is important to note that ISO 2768 applies only to features produced by machining or similar material-removal processes. It is most commonly associated with CNC machining, though its principles are referenced across many manufacturing contexts. The standard does not apply to features controlled by other standards, nor to raw material dimensions or reference dimensions on a drawing.

The Two Parts of ISO 2768 Explained

ISO 2768 is divided into two distinct parts, each addressing a different category of dimensional control. Understanding the distinction between them is essential before applying the standard to any drawing.

ISO 2768-1 covers general tolerances for linear and angular dimensions. This includes features such as external and internal lengths, diameters, heights, depths, steps, radii of curvature, and chamfer heights. It also covers angular dimensions expressed in degrees and minutes. Part 1 defines four tolerance classes — fine (f), medium (m), coarse (c), and very coarse (v) — each with progressively wider allowable variation as the class letter advances.

ISO 2768-2 addresses general geometric tolerances, including straightness, flatness, perpendicularity, symmetry, and run-out. Where Part 1 defines how much a measured dimension can deviate from its nominal value, Part 2 defines how much a feature's form or orientation can deviate from its ideal geometric condition. Part 2 uses three tolerance classes: H, K, and L, again progressing from tighter to looser control.

In practice, both parts are often referenced together in a single drawing notation. A drawing specifying "ISO 2768-mK," for example, applies medium linear tolerances (Part 1, class m) and tolerance class K geometric tolerances (Part 2). This dual-reference approach gives engineers flexible, comprehensive dimensional control with minimal annotation effort.

ISO 2768 Tolerance Classes: Fine, Medium, Coarse, and Very Coarse

The four tolerance classes in ISO 2768-1 define how tightly dimensions must be held across different ranges of nominal size. Each class assigns specific bilateral tolerance values that scale with the size of the feature — larger features are allowed greater absolute variation while maintaining proportional control. Here is how each class is characterized:

• Fine (f): The tightest general tolerance class. Intended for precision components where close fits or functional accuracy are important but full GD&T callouts are not warranted. Typical for precision machined parts used in instruments, medical devices, or tight-fitting assemblies.
• Medium (m): The most widely used class in general engineering. Balances dimensional control with manufacturing practicality. Suitable for the majority of machined components across industries including automotive, consumer electronics, and industrial equipment.
• Coarse (c): Applied to less critical features or components produced by less precise processes. Useful for structural parts, rough machined features, or features where the fit or function tolerates more variation.
• Very Coarse (v): Reserved for semi-finished or raw workpieces and features where significant variation is acceptable. Rarely used on finished machined parts; more applicable to castings, forgings, or preliminary operations.

To give a concrete example of how these classes translate into actual values: for a nominal linear dimension between 30 mm and 120 mm, the allowed tolerance is ±0.1 mm for class f (fine), ±0.2 mm for class m (medium), ±0.5 mm for class c (coarse), and ±1.0 mm for class v (very coarse). These values illustrate why class selection matters — the difference between fine and coarse represents a fivefold change in allowable variation for the same nominal size.

ISO 2768 Part 2: Geometric Tolerances

While Part 1 governs how close a measured dimension is to its nominal value, Part 2 governs the shape, orientation, and position of features. This is particularly important for assembled components where form errors — even if individual dimensions are within tolerance — can prevent proper fit or function.

ISO 2768-2 defines three geometric tolerance classes:

• Class H: The tightest geometric tolerance class. Applied to precision components requiring close geometric control, such as bearing housings, precision fixtures, or any part where surface straightness, flatness, or perpendicularity is functionally critical.
• Class K: A medium geometric tolerance class that covers the majority of general engineering applications. Provides adequate form control for most machined assemblies without imposing precision-level manufacturing requirements.
• Class L: The loosest geometric class, suitable for coarser applications, larger structural components, or secondary features where geometric deviation has minimal functional consequence.

As with Part 1, the tolerance values in Part 2 scale with the size range of the feature. Flatness and straightness tolerances, for example, tighten as part size decreases. Engineers should reference the full tolerance tables within the standard — or consult with their manufacturing partner — to confirm that the selected geometric class is appropriate for both the functional requirements and the manufacturing process being used.

When to Apply ISO 2768 General Tolerances

ISO 2768 is most effective as a baseline tolerance framework — a means of establishing sensible default variation for all features that do not require specific individual callouts. It should be applied when a significant portion of your drawing's features are non-critical or when the effort of annotating every dimension individually would add documentation burden without meaningfully improving manufacturing outcomes.

The standard is appropriate in the following situations:

• The part is produced by machining or a process where general machining tolerances are achievable without special attention.
• Many features on the drawing are non-functional or secondary (fillets, chamfers, general lengths) that do not require tight individual control.
• You are working with an established manufacturing partner familiar with ISO standards and able to confirm capability against the selected class.
• The part is in prototype or early-stage development and tighter individual tolerances will be specified only as functional requirements are validated.

Conversely, ISO 2768 alone is not sufficient when features have specific fit, clearance, or interference requirements that demand individual tolerance callouts — such as a shaft diameter running in a bearing, a press-fit pin, or a sealing surface. In these cases, ISO 2768 still serves a useful role as the general tolerance framework for all other features, while critical dimensions carry their own explicit tolerances. This combined approach is, in fact, the most common and most effective way to use the standard.

How to Call Out ISO 2768 on a Technical Drawing

The correct method for referencing ISO 2768 on a technical drawing is straightforward: include the standard designation in the drawing title block or general notes section, specifying both the Part 1 tolerance class and, if applicable, the Part 2 geometric tolerance class.

The format follows this pattern: ISO 2768-[Part 1 class][Part 2 class]. Examples include:

• ISO 2768-f — Fine linear and angular tolerances only (Part 1); no general geometric tolerance class specified.
• ISO 2768-m — Medium linear and angular tolerances (the most common single-part reference).
• ISO 2768-mK — Medium linear tolerances and class K geometric tolerances. A widely used combination for general engineering components.
• ISO 2768-fH — Fine linear tolerances and class H geometric tolerances. Appropriate for precision machined parts.
• ISO 2768-cL — Coarse linear tolerances and class L geometric tolerances. Used for less critical or structural components.

Once referenced in the title block, all dimensions on the drawing that do not carry an explicit individual tolerance are understood to be controlled by the specified ISO 2768 class. This keeps the drawing clean, reduces the chance of missed annotations, and communicates clearly with any manufacturer who works to ISO standards. When submitting drawings to your manufacturing partner, always confirm that the selected class is achievable with the intended process — particularly when working with tighter classes like f or H.

ISO 2768 Tolerance Classes Across Manufacturing Processes

ISO 2768 originated in a machining context, but tolerance class selection is influenced by whichever manufacturing process produces the part. Different processes have inherent dimensional capabilities that align more naturally with certain tolerance classes. Selecting a class that is incompatible with the process either forces expensive compensating measures or results in a high rejection rate.

For CNC machining, classes f (fine) and m (medium) are routinely achievable. CNC processes excel at maintaining tight dimensional control, making this pairing a natural fit for precision components across automotive, medical, and electronics applications.

For plastic injection molding, class m (medium) is a reasonable general starting point, though the achievable tolerance depends heavily on material, wall thickness, gate location, and tooling quality. Injection molded parts are subject to shrinkage and warpage, which means geometric tolerances from ISO 2768-2 are particularly important to evaluate carefully against the process capability.

For pressure die casting, class m to c (medium to coarse) is typical for most features, with tighter control achievable on critical machined or coined surfaces after casting. Die cast parts have higher inherent dimensional scatter than machined parts due to thermal contraction and die wear.

For sheet metal fabrication, class c (coarse) or m (medium) is generally appropriate for bent and formed features, though punched holes and laser-cut edges can achieve tighter control. The tolerance class selected should reflect the least capable operation on the drawing, with individual tolerances called out wherever tighter control is needed.

For processes like 3D printing and vacuum casting, ISO 2768 can be referenced as a baseline, but designers should verify process-specific capabilities with their manufacturing partner. Additive manufacturing processes, in particular, have layer-direction anisotropy that affects dimensional accuracy in ways the general ISO 2768 framework does not explicitly address.

Common Mistakes When Using ISO 2768

Understanding the standard is one thing; applying it correctly in production drawings is another. Several common errors can undermine the value of ISO 2768 or create quality problems downstream.

Selecting a class without verifying process capability. Specifying ISO 2768-f on a die cast part or a 3D printed prototype sets expectations that the process may not reliably meet. Always confirm achievable tolerances with your manufacturing partner before committing to a class on a drawing that will go into production.

Relying on ISO 2768 alone for critical features. General tolerances are not a substitute for specific GD&T callouts on functional features. Shafts, bores, mating surfaces, and any feature that directly affects assembly fit or product performance should carry explicit dimensional and geometric controls, not rely on the general class.

Omitting the geometric tolerance class (Part 2). Many engineers reference only ISO 2768-1 (the linear tolerance class) without specifying a Part 2 geometric class. This leaves form and orientation tolerances undefined for general features, which can create ambiguity in communication with manufacturers. Including both parts — for example, ISO 2768-mK — provides more complete coverage.

Applying ISO 2768 to non-machined processes without adjustment. The standard was written for machined parts. Applying it directly to castings, moldings, or formed sheet metal without acknowledging process-specific behavior can result in unrealistic expectations. Use ISO 2768 as a reference point, but discuss achievable tolerances with your manufacturing partner for any process other than machining.

Inconsistent application across a drawing set. If multiple drawings in a product assembly use different ISO 2768 classes without clear reasoning, manufacturing and inspection teams face unnecessary complexity. Establishing a company or project-level default class — with deviations applied only where justified — simplifies both documentation and quality control.

Conclusion

ISO 2768 general tolerances offer engineers a practical, internationally recognized framework for controlling dimensional variation without over-annotating technical drawings. By selecting an appropriate tolerance class — whether fine, medium, coarse, or very coarse for linear dimensions, paired with H, K, or L for geometric characteristics — you establish a clear baseline that governs every untoleranced feature on the drawing. This simplifies communication with manufacturers, reduces documentation effort, and supports consistent quality across the full production lifecycle.

The key to using ISO 2768 effectively is pairing it intelligently with your manufacturing process, reserving explicit individual tolerances for functionally critical features, and confirming that your selected class is achievable by your supplier. Applied this way, ISO 2768 becomes less of an administrative checkbox and more of a genuine design tool — one that aligns your engineering intent with real-world manufacturing capability from the very first drawing release.

At NICE Rapid, our engineering team works with customers across the full product development cycle, from early 3D printed prototypes to high-volume production runs, across processes including CNC machining, plastic injection molding, sheet metal fabrication, and more. If you have questions about tolerance class selection, drawing requirements, or process capability for your next project, our team is ready to help.