ISO 2768 General Tolerances

The ISO 2768-1 general tolerance classes for linear and angular dimensions, and which class a drawing should carry.

Page last changed 2026-10-19 · based on ISO 2768-1:1989

ISO 2768-1 Linear Tolerances (mm)

The class applies to every dimension that carries no tolerance of its own. That is the point of the system — it removes dozens of repeated tolerance notes from a drawing — and it is also why the choice is a cost decision. Changing a title block from 2768-m to 2768-f tightens every untoleranced dimension on the sheet at once, and on a part with many such dimensions that can multiply the machining cost.

The classes are cumulative in the sense that f is the tightest and v the loosest, but they are not interchangeable with the IT grades in ISO 286. An ISO 2768 tolerance applies to a general dimension; an IT grade applies to a specific feature of a fit. A drawing can correctly carry both — 2768-m in the title block, and an h7 callout on one bore.

Angular tolerances follow the same classes, with the tolerance set by the length of the shorter side of the angle — a short side amplifies the angular error into a larger linear one, so the standard keys the tolerance to the shorter leg rather than to the angle itself.

Which Class to Put on the Drawing

ISO 2768 does not specify which class to use — that is a design decision, and it is usually made once per drawing rather than per dimension.

f (fine) is for precision machinery where the untoleranced dimensions still matter — instrument parts, mating components, anything where a general dimension feeds into an assembly stack. It is appropriate where the shop is capable of it, and wasteful where it is not.

m (medium) is the default for general engineering. It is achievable by ordinary machining without special attention, and it is what most drawings should carry.

c (coarse) suits fabricated and welded assemblies, castings and any part where the untoleranced dimensions are genuinely unimportant — cut lengths, clearance holes, non-mating faces.

v (very coarse) is for heavy fabrication where thermal movement and handling make anything tighter meaningless.

A practical pattern is to put m in the title block and tighten individual dimensions with explicit tolerances or an IT callout where it matters. That gets the cost benefit of the loose default and the precision where the function needs it — the reverse approach, a tight general class with loose notes for the unimportant features, costs more and communicates less.

Note also ISO 2768-2, which covers geometrical general tolerances in classes H, K and L for straightness, flatness, perpendicularity and symmetry. A drawing can carry both 2768-1 and 2768-2 classes, and they are specified separately.

Frequently Asked Questions

What does ISO 2768-m mean?

It declares the medium general tolerance class, so every dimension on the drawing that has no tolerance of its own takes the medium-class value for its size range. Between 6 and 30 mm that is ±0.2 mm. It is the most common general tolerance class in general engineering.

What is the difference between ISO 2768-f and -m?

f is the fine class and m the medium one — f is roughly twice as tight at the same size. For a dimension between 30 and 120 mm, f allows ±0.15 mm and m allows ±0.3 mm. Choosing f tightens every untoleranced dimension on the drawing.

Is ISO 2768 still current?

ISO 2768-1:1989 and ISO 2768-2:1989 remain the published versions in general use, though they have been under revision for some years. Drawings specifying 2768-m are universally understood, and the replacement work is not yet published as an adopted standard.

How are angular general tolerances determined?

By the length of the shorter side of the angle, not by the angle itself. Under class m, an angle whose shorter side is up to 10 mm carries ±1°, while one with a shorter side over 400 mm carries ±0°5′. The rule exists because a short side turns a small angular error into a large linear one.

Can I use ISO 2768 on a drawing that also uses GD&T?

Yes, and it is common. The general tolerance covers untoleranced linear and angular dimensions; GD&T controls form, orientation, location and runout on the features where it is called out. The two operate on different dimensions and do not conflict — but a feature control frame does not absolve an untoleranced dimension from the general class.

Related

• ISO 286 Tolerance Chart
• Fits and Tolerances
• Hole and Shaft Limits
• GD&T Symbols
• Surface Texture Symbols

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

Data Sources

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Values apply to dimensions without individual tolerance indications. The class is declared in or near the title block and applies to the whole drawing. ISO 2768-2 geometrical general tolerances are declared separately and are not covered by the 2768-1 class.

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