Views: 237 Author: U-Need Publish Time: 2026-09-07 Origin: Site
Content Menu
● Why General Tolerances Matter in Manufacturing
● ISO 2768-1 Tolerance Classes
>> Fine Tolerance Class: ISO 2768-f
>> Medium Tolerance Class: ISO 2768-m
>> Coarse Tolerance Class: ISO 2768-c
>> Very Coarse Tolerance Class: ISO 2768-v
● ISO 2768-1 Linear Tolerance Table
>> Example: ISO 2768-m for an 80 mm Dimension
● ISO 2768-2 Geometrical Tolerance Classes
>> Common ISO 2768 Drawing Notes
● How to Apply ISO 2768 on Engineering Drawings
>> Identify Critical Dimensions First
>> Use General Tolerances for Non-Critical Features
>> State Additional Requirements Separately
>> Features That Often Need Explicit Tolerances
>> How Tight Tolerances Affect CNC Machining Cost
● ISO 2768 for Mold Manufacturing
>> Key Mold Design Considerations
● ISO 2768 for Stamping and Cold-Forging Dies
>> Factors That Affect Tooling Accuracy
● ISO 2768 for Sheet Metal Fabrication
>> Sheet Metal Features That Need Special Attention
>> Sheet Metal Tolerance Considerations
● ISO 2768 and GD&T: When General Tolerances Are Not Enough
>> Use Explicit Geometric Controls When Needed
● Common ISO 2768 Mistakes to Avoid
>> Missing the General Tolerance Note
>> Over-Tolerancing Every Feature
>> Using General Tolerances for Hole Position
>> Ignoring Surface Finish Requirements
>> Forgetting Thread Specifications
>> Applying Machining Tolerances to Formed Parts
>> Not Reviewing Assembly Tolerance Stack-Up
● Practical Drawing Review Checklist
● Summary
>> What does ISO 2768-mK mean?
>> Is ISO 2768-mK suitable for CNC machining?
>> Does ISO 2768 apply to threads?
>> Does ISO 2768 control hole position?
>> Which ISO 2768 class is best for sheet metal fabrication?
>> Is ISO 2768-fH better than ISO 2768-mK?
>> Can ISO 2768 and GD&T be used together?
ISO 2768 is a widely used general tolerance standard for technical drawings. It helps engineers, buyers, and manufacturers define acceptable dimensional and geometrical variation when individual tolerances are not specified for every feature.
For global manufacturing projects involving custom CNC machining, injection molds, stamping dies, cold-forging dies, laser cutting, bending, and sheet metal fabrication, a clear tolerance strategy prevents costly misunderstandings. It gives production teams a shared interpretation of drawings, reduces unnecessary inspection requirements, and helps balance part performance with manufacturing cost.
At U-Need, we support global brands, distributors, and manufacturers with end-to-end precision manufacturing solutions in China. In day-to-day project reviews, the same issue often appears: a part drawing includes dimensions but does not clearly explain how much variation is acceptable. ISO 2768 provides a practical starting point, but it must be combined with sound engineering judgment.
ISO 2768 is a general tolerance standard used on engineering drawings. It establishes default permissible deviations for dimensions and geometric features that do not have individually stated tolerances.
Instead of adding a separate tolerance to every dimension, a drawing can include a general note such as:
GENERAL TOLERANCES: ISO 2768-mK
UNLESS OTHERWISE SPECIFIED
This note tells the manufacturer how to interpret untoleranced dimensions and selected geometric characteristics.
For example, a drawing may show:
Length: 80 mm
Without an individual tolerance, the acceptable manufacturing range depends on the ISO 2768 class specified in the drawing title block.
ISO 2768 is divided into two primary parts:
| Standard | Main Application | Tolerance Classes |
|---|---|---|
| ISO 2768-1 | Linear and angular dimensions without individual tolerance indications | f, m, c, v |
| ISO 2768-2 | General geometrical tolerances for selected features without individual tolerance indications | H, K, L |
The first part addresses dimensional variation. The second part addresses selected geometric requirements, such as straightness, flatness, perpendicularity, symmetry, and circular run-out.
A correctly applied ISO 2768 note makes drawings easier to read and less repetitive. It also gives manufacturing teams a defined baseline before they begin process planning, fixture design, machining, inspection, or assembly.
A dimension alone does not tell a manufacturer how accurate a feature must be. A 50 mm dimension may be acceptable at 49.8 mm in one application but unacceptable in another.
If a drawing does not show individual tolerances or a general tolerance standard, suppliers may interpret the same feature differently. This creates variation in quoted cost, manufacturing approach, inspection standards, and finished-part quality.
Clear general tolerances help reduce problems such as:
- Assembly interference between mating components
- Excessive gaps in enclosures and fabricated structures
- Misaligned mounting holes
- Unstable part quality between production batches
- Delays during sample approval
- Disputes during incoming inspection
- Unnecessary manufacturing cost caused by over-tolerancing
For a sourcing team, tolerances directly influence the quotation process. Tight tolerances can require slower machining cycles, additional setups, specialized cutters, more complex fixtures, temperature-controlled inspection, and detailed measurement reports.
For a manufacturing team, tolerances determine which process is appropriate. A CNC-machined aluminum component can often hold tighter dimensions than a bent sheet metal bracket. A molded plastic part may be affected by shrinkage and warpage. A welded assembly may change shape because of heat distortion.
The goal is not to specify the tightest possible tolerance. The goal is to specify the widest tolerance that still allows the part to perform correctly.
ISO 2768-1 applies to linear and angular dimensions that do not have individual tolerances.
The standard uses four tolerance classes:
| Class | Meaning | Typical Applications |
|---|---|---|
| f | Fine | Precision-machined components, close-fit interfaces, high-accuracy parts |
| m | Medium | General CNC-machined parts, housings, brackets, fixture plates, mechanical assemblies |
| c | Coarse | Sheet metal components, fabricated parts, non-critical castings, welded structures |
| v | Very coarse | Large fabrications, rough structural parts, low-precision applications |
The fine class is used when features require relatively tight control but do not need individual tolerances throughout the drawing.
It may be suitable for:
- Precision-machined spacers
- Mechanical alignment features
- Compact components with close interfaces
- Small parts with controlled fit requirements
- Certain tooling and fixture components
Fine general tolerances can raise manufacturing and inspection requirements. They should be selected only when product performance justifies the additional effort.
The medium class is one of the most commonly used options for general CNC machining. It provides a practical balance between dimensional consistency and manufacturing efficiency.
It is often suitable for:
- Aluminum and steel machined housings
- Mounting brackets
- Machine components
- Fixture plates
- General mechanical assemblies
- Equipment panels
- Standard industrial hardware
For many custom CNC machining projects, ISO 2768-m is a reliable starting point. Critical features can then receive individual tolerances where necessary.
The coarse class is often appropriate for processes with greater natural variation, including sheet metal bending, welding, casting, and large structural fabrication.
It may be used for:
- Laser-cut and bent sheet metal parts
- Welded frames
- Support brackets
- Large equipment covers
- Non-critical formed components
- General industrial fabrications
Using a coarse tolerance does not mean the part is low quality. It means the specified dimensional variation matches the functional needs and normal behavior of the manufacturing process.
The very coarse class is generally used for large, simple, or non-critical fabrications where tight control is unnecessary.
Typical applications include:
- Large structural components
- Heavy equipment frames
- Rough-cut fabricated parts
- Non-critical support structures
- Large welded assemblies
This class is rarely appropriate for small precision components, close assemblies, or parts containing mating features.
The following table shows common general tolerances for linear dimensions other than broken edges, external radii, and chamfer heights.
| Nominal Size Range | Fine f | Medium m | Coarse c | Very Coarse v |
|---|---|---|---|---|
| 0.5 to 3 mm | ±0.05 mm | ±0.10 mm | ±0.20 mm | — |
| Over 3 to 6 mm | ±0.05 mm | ±0.10 mm | ±0.30 mm | ±0.50 mm |
| Over 6 to 30 mm | ±0.10 mm | ±0.20 mm | ±0.50 mm | ±1.00 mm |
| Over 30 to 120 mm | ±0.15 mm | ±0.30 mm | ±0.80 mm | ±1.50 mm |
| Over 120 to 400 mm | ±0.20 mm | ±0.50 mm | ±1.20 mm | ±2.50 mm |
| Over 400 to 1,000 mm | ±0.30 mm | ±0.80 mm | ±2.00 mm | ±4.00 mm |
| Over 1,000 to 2,000 mm | ±0.50 mm | ±1.20 mm | ±3.00 mm | ±6.00 mm |
| Over 2,000 to 4,000 mm | — | ±2.00 mm | ±4.00 mm | ±8.00 mm |
Suppose a drawing includes the following dimension:
the individual tolerance takes priority over the general ISO 2768-m tolerance.
ISO 2768-2 applies to selected geometrical characteristics when no individual geometric tolerance is specified.
It uses three classes:
| Class | General Precision Level | Typical Applications |
|---|---|---|
| H | Fine | Precision interfaces, accurate machined surfaces, alignment-sensitive components |
| K | Medium | General CNC-machined parts and standard mechanical assemblies |
| L | Coarse | Sheet metal fabrications, welded structures, non-critical formed components |
These general geometric controls can apply to characteristics including:
- Straightness
- Flatness
- Perpendicularity
- Symmetry
- Circular run-out
The class chosen should match the part's function, material, manufacturing method, size, and inspection requirements.
For example, a machined sealing face may need a specific flatness requirement. A basic ISO 2768-K note may not provide enough control for a surface that must prevent fluid leakage. In that case, the drawing should include an individual flatness callout.
Similarly, a shaft location that affects bearing alignment should not rely only on a general geometric tolerance. It may require clearly identified datums and explicit geometric controls.
ISO 2768-mK is a combined general tolerance designation. It is commonly used on mechanical and fabricated-part drawings because it provides general dimensional and geometrical requirements in one concise note.
The two characters refer to different parts of the standard:
| Symbol | Meaning |
|---|---|
| m | Medium class for untoleranced linear and angular dimensions |
| K | Medium class for applicable untoleranced geometrical characteristics |
A title-block note may read:
GENERAL TOLERANCES: ISO 2768-mK
UNLESS OTHERWISE SPECIFIED
This means that untoleranced linear and angular dimensions follow the medium class of ISO 2768-1, while applicable untoleranced geometric features follow the K class of ISO 2768-2.
The capitalization should be retained:
- Use lowercase letters for dimensional tolerance classes: f, m, c, v
- Use uppercase letters for geometric tolerance classes: H, K, L
| Drawing Note | Suitable Use |
|---|---|
| ISO 2768-fH | High-accuracy machined parts and precision tooling components |
| ISO 2768-mK | General CNC machining, housings, brackets, fixtures, and mechanical components |
| ISO 2768-cL | Sheet metal fabrication, welded structures, castings, and non-critical formed parts |
| ISO 2768-m | Drawings that use individual geometric tolerances for critical features |
For many industrial parts, ISO 2768-mK offers a useful balance. It avoids excessive tolerancing while still providing a clear framework for manufacturing and inspection.
A well-prepared drawing should help a supplier understand three things immediately:
1. Which dimensions are critical.
2. Which dimensions follow the general tolerance standard.
3. Which additional material, surface, and inspection requirements apply.
Before applying a general tolerance class, identify dimensions that affect product function.
Critical features often include:
- Bearing bores
- Press-fit diameters
- Threaded interfaces
- Sealing surfaces
- Connector openings
- Mating-hole patterns
- Shaft locations
- Alignment pins
- Sliding surfaces
- Safety-related interfaces
- Electrical or optical alignment features
These dimensions should normally receive individual tolerances.
For example:
Bearing Bore: Ø25.000 +0.021 / 0.000 mm
Connector Cutout: 14.00 ±0.05 mm
Sealing Face Flatness: 0.05 mm
Hole Position: Ø0.10 mm Relative to Datums A | B | C
Non-critical features can often follow an ISO 2768 class.
These may include:
- External part length
- Overall width
- Non-functional pockets
- Basic wall dimensions
- External edges
- Cosmetic profiles
- Clearance features
- General mounting surfaces
This approach makes drawings cleaner and easier to review.
ISO 2768 does not replace other manufacturing instructions. A complete drawing should also define requirements for:
- Material grade
- Surface finish
- Heat treatment
- Plating or coating
- Anodizing
- Thread type and class
- Deburring
- Edge-break condition
- Welding requirements
- Marking or engraving
- Cosmetic surface requirements
- Inspection documents
For example:
Material: Aluminum 6061-T6
Finish: Clear Anodizing
General Tolerances: ISO 2768-mK
Threads: M4 × 0.7-6H
Surface Roughness: Ra 1.6 max on sealing face
Deburr All Edges: Break Sharp Edges 0.2–0.5 mm
A drawing with this level of information is easier to quote, manufacture, inspect, and approve.
CNC machining can produce tight and repeatable dimensions when the part design, material, tool access, workholding, machine capability, and inspection method are appropriate.
For general machined components, ISO 2768-mK is often a reasonable baseline. It is particularly useful for parts such as:
- Aluminum housings
- Steel brackets
- Fixture plates
- Machine covers
- Motor mounts
- Sensor mounts
- Industrial equipment components
- Robotic parts
- Automation hardware
- Custom mechanical assemblies
However, not every feature on a CNC-machined part should receive the same tolerance.
The following features commonly need tighter control than a general ISO 2768 note can provide:
- Bearing seats
- Precision bores
- Gear interfaces
- Press-fit holes
- Critical shafts
- Sealing grooves
- O-ring grooves
- Optical mounting surfaces
- Precision slot widths
- Hole patterns for mating assemblies
- Datum surfaces
- High-flatness mounting interfaces
Tighter tolerances can increase cost for several reasons:
- More precise workholding may be required.
- Machining may require additional finishing passes.
- Tools may need more frequent inspection or replacement.
- Operators may need to perform in-process measurement.
- Parts may require CMM inspection.
- Scrap risk may increase.
- Production cycle times may become longer.
A practical drawing avoids making every dimension critical. Instead, it protects the features that determine fit, function, safety, and product quality.
Mold manufacturing requires a different tolerance mindset because the finished tool and the final molded part are both important.
Injection molds contain precision elements such as:
- Core and cavity inserts
- Slide mechanisms
- Ejector components
- Parting-line surfaces
- Shut-off faces
- Cooling channels
- Gate areas
- Guide pins and bushings
- Mold bases
- Textured or polished surfaces
For mold tooling, ISO 2768 may be useful for non-critical base components and general features. However, critical mold elements often require individually specified tolerances.
When defining tolerances for injection mold manufacturing, engineers should consider:
- Resin shrinkage
- Mold temperature
- Wall thickness variation
- Part geometry
- Gate location
- Cooling design
- Warpage risk
- Required surface appearance
- Tool steel selection
- Expected production volume
A mold may be machined accurately, but the molded part can still vary because of material behavior and molding conditions. Therefore, tolerance planning should connect tool geometry, resin properties, and final part function.
Stamping dies and cold-forging dies often contain high-wear, high-load features that require precise dimensional and geometric control.
Important tooling features may include:
- Punches
- Dies
- Pilots
- Guide systems
- Cutting edges
- Clearances
- Forming surfaces
- Die inserts
- Alignment components
- Replaceable wear parts
General tolerances can be used for non-critical tooling features. However, critical cutting clearances, die alignment, punch positions, and mating interfaces should be individually controlled.
Tooling accuracy is influenced by more than the original drawing. Production performance may also depend on:
- Tool steel grade
- Heat treatment
- Surface treatment
- Material thickness
- Workpiece hardness
- Lubrication
- Press capability
- Tool wear
- Maintenance intervals
- Part ejection conditions
A robust die design considers both initial precision and long-term repeatability.
Sheet metal fabrication usually involves processes such as laser cutting, punching, bending, forming, welding, grinding, and assembly.
Because bending and welding can introduce variation, general tolerances for sheet metal should reflect process reality.
For many non-critical sheet metal components, ISO 2768-cL may be more appropriate than ISO 2768-mK.
Some features should receive individual tolerances because they directly affect assembly or product function:
- Connector cutouts
- Display openings
- Mounting-hole patterns
- PEM insert locations
- Hinge interfaces
- Door gaps
- Mating flanges
- Sealing surfaces
- Structural mounting points
- Bracket interfaces
The following factors affect final sheet metal dimensions:
- Material thickness
- Material grade
- Bend angle
- Inside bend radius
- Grain direction
- Bend sequence
- Springback
- Tooling condition
- Welding distortion
- Coating thickness
- Part size
For example, a laser-cut mounting hole may be highly repeatable, but the same hole's location after multiple bends can shift relative to the finished assembly. The drawing should control the functional relationship that matters in the final formed condition.
General tolerances provide a useful baseline, but they do not replace a full geometric dimensioning and tolerancing system for complex or highly functional parts.
Geometric dimensioning and tolerancing is especially valuable when a part must assemble accurately relative to defined datum surfaces or axes.
It is often appropriate for:
- Multi-hole patterns
- Bearing housings
- Precision fixture components
- Rotating shafts
- Automotive components
- Medical-device parts
- Aerospace components
- Optical equipment
- Robotic systems
- Sealing assemblies
- Complex multi-part assemblies
Explicit geometric controls are valuable when a drawing needs to define:
- True position
- Parallelism
- Perpendicularity
- Concentricity
- Cylindricity
- Profile
- Run-out
- Datum relationships
- Critical surface flatness
A practical strategy is to combine both methods:
- Use ISO 2768 for ordinary untoleranced dimensions.
- Use explicit tolerances for critical dimensions.
- Use datums and geometric controls for assembly-critical relationships.
This approach keeps the drawing understandable while protecting the most important functional requirements.
A drawing without a general tolerance note creates uncertainty. Different suppliers may make different assumptions, leading to inconsistent quotations and inspection expectations.
Adding tight tolerances to all dimensions can increase production cost without improving the product. Tight control should be reserved for features that affect function.
Hole diameter and hole location are different requirements. A hole may have the correct size but still fail to align with its mating component. Use datum-based controls for critical patterns.
Dimensional accuracy is only one part of part quality. A sealing face, sliding surface, cosmetic panel, or coated component may need a stated surface finish requirement.
Threads should include complete details such as size, pitch, depth, tolerance class, and any special requirements. General tolerances do not define thread fit.
A tight CNC-machining tolerance may not be practical for a bent or welded sheet metal part. Match the tolerance class to the manufacturing process.
A single part can meet its drawing but still create assembly problems when multiple tolerances accumulate. Review interfaces across the full product assembly, especially for hole patterns, stacks, enclosures, seals, and moving components.
Before releasing a drawing for quotation or production, review the following points:
- Confirm that the drawing includes a general tolerance note.
- Select a tolerance class that matches the manufacturing process.
- Use ISO 2768-mK as a starting point for many general CNC-machined components.
- Consider ISO 2768-cL for non-critical sheet metal fabrications and welded structures.
- Apply explicit tolerances to critical dimensions.
- Identify datum surfaces for assembly-critical features.
- Define material grade and condition.
- Specify surface finish where performance or appearance requires it.
- State coating, plating, anodizing, or heat-treatment requirements.
- Include thread specifications and depths.
- Define deburring and edge-break requirements.
- Identify cosmetic surfaces and acceptable visual standards.
- Provide 2D drawings and 3D CAD models.
- Review the complete assembly for tolerance stack-up risk.
- Confirm inspection requirements before production begins.
A detailed drawing review before manufacturing can prevent rework, reduce sampling delays, and improve consistency across prototypes and production batches.
ISO 2768 is a practical method for communicating general dimensional and geometrical tolerance requirements on engineering drawings. It helps reduce repetitive tolerance notes, improves consistency between suppliers, and supports more efficient manufacturing planning.
For many custom CNC-machined parts, ISO 2768-mK provides a balanced starting point. For sheet metal fabrication, welded structures, and non-critical formed components, a coarser approach such as ISO 2768-cL may be more practical.
The strongest drawings combine general tolerances with explicit requirements for critical dimensions, mating features, surface finish, threads, material properties, and geometric relationships. This helps ensure that every feature receives the right level of control.
U-Need supports custom precision parts machining, injection mold manufacturing, stamping dies, cold-forging dies, laser cutting, sheet metal bending, and metal stamping for global manufacturing projects. Sharing complete 2D drawings, 3D CAD files, material specifications, and quality requirements early in the project helps create a more accurate manufacturing plan and a smoother transition from prototype to production.
ISO 2768-mK combines two general tolerance classes. The lowercase m indicates the medium class for untoleranced linear and angular dimensions. The uppercase K indicates the medium class for applicable untoleranced geometric characteristics.
Yes. ISO 2768-mK is commonly suitable for general CNC-machined parts such as brackets, housings, fixture plates, and mechanical components. Critical dimensions, bearing fits, sealing surfaces, and important hole positions should still receive individual tolerances.
No. ISO 2768 does not define thread type, pitch, thread class, or thread fit. Drawings should separately specify full thread requirements.
ISO 2768 provides general dimensional and selected geometric requirements, but it does not replace datum-based position control for assembly-critical hole patterns. Where alignment matters, use explicit position tolerances and datum references.
For many non-critical sheet metal parts, ISO 2768-cL can be suitable because forming, bending, and welding naturally introduce more variation than CNC machining. Critical holes, cutouts, mating flanges, and interfaces should receive individual tolerances.
Not necessarily. ISO 2768-fH is tighter and may increase machining time, inspection effort, and manufacturing cost. It should be selected only when the part's function requires fine dimensional and geometric control.
Yes. A common drawing strategy is to use ISO 2768 for ordinary untoleranced dimensions while adding explicit dimensional tolerances and geometric controls to features that affect assembly, alignment, sealing, motion, or safety.
1. International Organization for Standardization. "ISO 2768-1:1989 — General Tolerances: Part 1: Tolerances for Linear and Angular Dimensions Without Individual Tolerance Indications."
[https://www.iso.org/standard/7748.html]
2. International Organization for Standardization. "ISO 2768-2:1989 — General Tolerances: Part 2: Geometrical Tolerances for Features Without Individual Tolerance Indications."
[https://www.iso.org/standard/7749.html]
3. ASME. "Y14.5 Dimensioning and Tolerancing."
[https://www.asme.org/codes-standards/find-codes-standards/y14-5-dimensioning-tolerancing]
4. ZEISS Quality Forum. "ISO 2768-1 and ISO 2768-2 General Tolerances Chart."
[https://qualityforum.zeiss.com/migration/images/137_8bb2b6eeb6a9e6554d254c216a890c89.pdf]
5. RpProto. "ISO 2768 Tolerance Standard: Classes, Tables & How to Apply."
[https://www.rpproto.com/blog/iso-2768-tolerance-guide]
6. Camcut Group. "General Tolerances for Angular Dimensions."
