ISO 2768 General Tolerances: Full Tables, Classes, and ISO 2768-mK Explained

ISO 2768 — formally General tolerances — exists to solve a simple drafting problem: most dimensions on a machined part do not need an individually written tolerance. Writing ±0.1 next to every one of 200 dimensions clutters the drawing, slows drafting, and invites errors. ISO 2768 lets the designer write one note and have a published table fill in the rest. The standard applies to parts produced by metal removal and parts formed from sheet metal, and it covers exactly the dimensions that carry no individual tolerance indication. Anything that matters functionally still gets its own callout, which overrides the general class for that feature.

The standard is built on the idea of customary workshop accuracy: the tolerance a competent shop holds in normal production without special effort. A shop is expected to know its customary accuracy and to accept only drawings whose general class is equal to or looser than it. That is why class m maps so well onto ordinary CNC milling and turning — for how those process-level capabilities translate into achievable tolerances, see our guide to CNC machining tolerances. Published in 1989 in two parts, ISO 2768-1 (linear and angular dimensions) remains current, while ISO 2768-2 (geometrical tolerances) was withdrawn in 2021 and replaced by ISO 22081:2021 — a status change covered in the Part 2 section below.

The commercial benefit is real on both sides. Buyers get shorter, clearer drawings and fewer inspection dimensions. Suppliers get an unambiguous default instead of having to guess what an untoleranced dimension means — or worse, quote conservatively because the drawing is silent. When both parties reference the same table, “machine it to the print” has one meaning.

Broken edges get their own table because external radii and chamfer heights rarely carry functional weight proportional to a tight class. Note that f and m are identical here, as are c and v — upgrading a drawing from m to f buys nothing on edge breaks.

Angular dimensions follow the same four-class logic, but the deviation is driven by the length of the shorter side of the angle, not the angle value itself — a sensible rule, since a given angular error produces more linear displacement over a longer leg. Deviations are stated in degrees and minutes.

Again f and m are identical across all five bands, so the practical choice is between m (±30′ on a typical 10–50 mm leg), c, and v. Right angles count as angular dimensions under this table unless the drawing invokes the geometrical classes of Part 2. If a chamfer or angle is functional — a sealing bevel, a mating lead-in, an optical mounting face — write its tolerance individually rather than relying on the class.

The designation combines one letter from each part: the lowercase letter (f/m/c/v) picks the size class from Part 1, the uppercase letter (H/K/L) picks the geometrical class from Part 2. ISO 2768-mK — medium size, medium geometry — is the de facto global default for machined parts and the note you will see most often on drawings from European and Chinese suppliers alike. European drawings commonly show “ISO 2768-mK” or the older national adoption “DIN ISO 2768-mK.” Chinese drawings frequently carry the domestic equivalent: GB/T 1804, which is technically equivalent to ISO 2768, so a note reading “未注公差按 GB/T 1804-m” (untoleranced dimensions per GB/T 1804, class m) means the same table values as ISO 2768-m. If you are decoding the rest of the symbols around that note, our engineering drawing symbols reference covers the full vocabulary.

Two clauses of the standard deserve attention because few buyers read them. Clause 6 says a workpiece that exceeds the general tolerance is not automatically rejected if its function is unimpaired. Acceptance becomes a functional question, not a metrology question, unless the drawing or purchase order explicitly overrides the clause. And Annex A places a duty on the workshop: know your customary accuracy, and only accept drawings whose general class is at or above it. Together these clauses make ISO 2768 a contract about process capability, not just a lookup table — which is why serious shops state the class they hold in their quality documentation.