Key takeaways
- A general tolerance only applies if the drawing cites it; with no callout, untoleranced dimensions are open to argument.
- In “ISO 2768-mK”, the lowercase letter is the class for linear and angular sizes and the capital letter is the class for geometry.
- ISO 2768-2 was withdrawn and replaced by ISO 22081:2021, so agree with the supplier which standard the drawing means.
- ISO 2768-1 applies to machined and sheet-metal parts; castings have their own general tolerances in ISO 8062-3.
- A dimensional inspection measures sampled parts against the drawing, including the general tolerance class.
What ISO 2768 is for
Engineering drawings show many dimensions. Giving each one its own tolerance would clutter the drawing. A general tolerance standard sets default limits for every dimension that has no individual tolerance, and the drawing cites it once, usually in or near the title block.
| Standard | Covers | Classes | Status (ISO, Oct 2026) |
|---|---|---|---|
| ISO 2768-1:1989 | Linear and angular dimensions without individual tolerance indications, for parts made by metal removal or formed from sheet metal | f (fine), m (medium), c (coarse), v (very coarse) | Published; last confirmed 2022; a revised ISO 2768 is under development |
| ISO 2768-2:1989 | Geometrical tolerances (such as straightness, flatness, perpendicularity) for features without individual indications, mainly for parts made by removal of material | H, K, L | Withdrawn; revised by ISO 22081:2021 |
| ISO 22081:2021 | Rules for defining and interpreting general geometrical specifications and general size specifications under the ISO GPS system | See the standard | Published; confirmed 2026 |
The ISO 2768 tables themselves are paid content. Buy the standard, or ask the buyer for the values that apply, before agreeing a sampling plan.
How to read “ISO 2768-mK” on a drawing
The callout combines the two parts of ISO 2768:
- ISO 2768 names the standard.
- m is the ISO 2768-1 class for linear and angular sizes: medium. The tolerance band widens as the nominal size grows, and widens again from f to m to c to v.
- K is the ISO 2768-2 class for geometrical tolerances. H is the tightest of the three and L the loosest.
Other common forms are “ISO 2768-f” (sizes only, fine class) and “ISO 2768-cL”. A drawing that cites only part 1 sets no general geometrical tolerance.
Three points cause disputes:
- No callout. If the title block cites no general tolerance standard, untoleranced dimensions have no agreed limit. Settle this before production, not at the final inspection.
- Withdrawn part 2. ISO 2768-2 is withdrawn, but drawings still cite it. Some buyers have moved to ISO 22081, which works differently. Confirm in writing which one the drawing means.
- Wrong process. ISO 2768-1 is written for machined and sheet-metal parts. For castings, ISO 8062-3:2023 gives general dimensional and geometrical tolerances and machining allowances. Wood and furniture parts usually need the buyer's own tolerances.
Why it matters for engineering exports from India
India supplies machined parts, castings, forgings, sheet-metal fabrications and furniture hardware to buyers who send drawings with an ISO general tolerance block. Problems usually come from the gap between the drawing and the shop floor:
- Drawings not shared with sub-contractors. A machining job-worker may receive a sketch with key dimensions only, and never see the general tolerance class.
- Class misunderstood. “mK” read as one class, or the geometry class ignored, so flatness and squareness are never checked.
- Measuring tools that cannot resolve the tolerance, such as a steel rule used where a fine class needs a caliper or micrometer.
- Cast surfaces measured against machined tolerances, or the reverse, because the drawing does not state which standard applies to which feature.
- Drawing revision changes that reach the buyer's engineer but not the factory.
For furniture hardware such as brackets, hinges and fittings, the general tolerance controls fit with the wood parts. A bracket that is in tolerance on paper but out on hole spacing will still stop assembly.
What a dimensional inspection checks
| An inspector at the factory can check | Needs a metrology lab or CMM |
|---|---|
| The latest drawing revision is in use and cites a general tolerance standard and class | Complex geometrical tolerances such as profile, position to datums or form on large parts |
| Critical and general dimensions on sampled parts with calipers, micrometers, height gauges, pin and thread gauges | Measurement uncertainty studies and gauge calibration |
| Flatness, straightness and squareness with a surface plate, feeler gauges and squares, where the class allows | Full first-article layout reports on many features |
| Calibration labels and certificates on the factory's own gauges | Material properties (see mill test certificates) |
Sampling follows the agreed plan, usually an AQL table. See AQL sampling explained and try the AQL calculator.
How Clear To Load checks this in India
On a pre-shipment inspection in India or a during-production inspection, the inspector measures sampled parts against your drawing and its general tolerance class, records each reading, and photographs the gauges used. Send us the drawing and tell us which dimensions are critical. Where a part needs a coordinate measuring machine, we can arrange for samples to go to an accredited lab of your choice.
The report arrives within 24 hours and ends in a verdict: Cleared to load, Hold or Not cleared. Book an inspection to add these checks.