ISO 22081 — General Geometrical Tolerances Reference

Context

Why ISO 2768-2 was withdrawn

ISO 2768-2 served engineers well for decades, but it had a fundamental limitation: it forced designers to accept a committee's pre-defined tolerance values for every geometric characteristic. ISO 22081 corrects this by moving to a designer-specified model.

ISO 2768-2 — Withdrawn approach

Pre-defined H/K/L tolerance class tables in the standard
Single class letter covers all geometric characteristics simultaneously
No way to specify flatness at one tolerance and perpendicularity at another
No datum references possible in general tolerances
Standalone — not integrated with the GPS framework
Abstract: designers must look up what "K" means per characteristic

ISO 22081:2021 — Current approach

Designer specifies tolerance values directly — no lookup table needed
Each geometric characteristic can have its own tolerance value
Different tolerances for flatness vs perpendicularity vs run-out
Optional datum references can be included
Fully integrated with ISO GPS: uses ISO 1101 symbols and syntax
Explicit: the tolerance value is right there in the title block

ISO 2768-1 is unaffected

Only the geometrical part (Part 2) was withdrawn. ISO 2768-1 — general tolerances for linear and angular dimensions — remains active and in widespread use. The f/m/c/v tolerance classes for linear dimensions are still valid for new drawings.

ISO 22081 — Fundamentals

The core concept

ISO 22081 is built on one idea: general geometrical tolerances are simply default tolerances that apply to all features on a drawing unless a tighter (or different) individual tolerance is specified. They are expressed using exactly the same language as individual tolerances — ISO 1101 feature control frames.

1

General tolerance indicator in the title block

A special box is added to the drawing title block (or general notes area). It contains one or more rows, each specifying a geometric characteristic and its default tolerance value — optionally with a datum reference.

2

Applies to all untoleranced features

Every feature on the drawing that does not carry an individual feature control frame automatically inherits the general tolerance for that characteristic. If a feature has its own callout, that takes precedence — the general tolerance is only the default fallback.

3

Each characteristic is independent

You can specify different values for different characteristics. For example: flatness 0.1 mm, perpendicularity 0.2 mm, position 0.5 mm. With ISO 2768-2, one class letter fixed all of them together.

4

Datums are optional but allowed

For orientation and location characteristics (perpendicularity, parallelism, position), the general tolerance indicator can include a datum reference. This tells the shop which datum to use when verifying general orientation/location tolerances on untoleranced features.

Title block

The general tolerance indicator

The general tolerance indicator is the physical container in the title block that holds all the general geometrical tolerance specifications. It looks like a compact feature control frame table.

Minimum required content

The general tolerance indicator must include at minimum: the standard designation (ISO 22081), the geometric characteristic symbol (ISO 1101), and the tolerance value. The datum column is included only when a datum reference applies to that characteristic.

Can be combined with ISO 2768-1

ISO 22081 for geometrical tolerances and ISO 2768-1 for linear/angular tolerances are used together on the same drawing. The title block carries both: ISO 2768-m for linear/angular general tolerances, and the ISO 22081 indicator box for geometrical general tolerances.

In practice

Applying ISO 22081 on drawings

The general tolerance indicator lives in or adjacent to the title block. Here is the correct placement, scope rules, and how it interacts with individually toleranced features.

ISO 22081 — Application rules
Rule	Detail
Precedence	Individual feature control frames always take precedence over general tolerances. The general tolerance indicator is only the fallback for features with no individual callout.
Scope	The general tolerance indicator applies to the entire drawing unless a feature or view is explicitly excluded. There is no partial scope by area.
Datum identification	Datum features referenced in the general tolerance indicator must be identified on the drawing using ISO 5459 datum feature symbols in the usual way.
Combining with ISO 2768-1	Both are stated in the title block: `ISO 2768-m` for linear/angular, plus the ISO 22081 indicator table for geometrical. These two systems govern different types of tolerances and do not conflict.
No tolerance classes	There are no predefined tolerance classes in ISO 22081. The tolerance values are chosen by the designer based on functional requirements and process capability.
Multiple characteristics	Each geometric characteristic type gets its own row. You can have general flatness at 0.1 mm, general perpendicularity at 0.3 mm, and general circular run-out at 0.2 mm all on the same indicator.
Not all characteristics required	Only specify characteristics that are functionally relevant. If there are no general perpendicularity requirements beyond what ISO 2768-1 already controls, simply omit perpendicularity from the indicator.

The key mindset shift

ISO 22081 forces you to think about what you actually need. With ISO 2768-2, writing mK in the title block took no thought — the values were pre-assigned. With ISO 22081, you must decide the tolerance for each characteristic deliberately. That is the point of the change, and it is where most engineers need to build new habits.

Want to go deeper?

Practical case studies & real drawings.

ISO 22081 is straightforward in theory — the challenge is applying it correctly on real parts, coordinating it with your datum scheme, and migrating legacy drawings without introducing errors. That is exactly what we cover in sessions and training.

Book a 1-on-1 session → Register for training →