4/ Centring tolerance

Code 4/ limits the tilt of a surface relative to the datum axis. It is written in the field of the surface it applies to.

Standard: ISO 10110-6

Decode a callout →Use it in a drawing →Build a 4/ callout

Syntax

4/σ	σ = max. surface tilt angle: the angle between the datum axis and the surface normal where they meet. Always write the unit (′ or ″).
4/σ(L)	Aspheres: L = max. lateral displacement of the asphere’s axis from the datum axis, in mm.

Worked examples

4/ 3′	Surface tilt ≤ 3 arcminutes.
4/ 30″	Surface tilt ≤ 30 arcseconds.
4/ 3'(0.01)	Asphere: tilt ≤ 3′ and lateral displacement ≤ 0.01 mm.

Click an example to open it in the decoder.

Common values and typical grades

Commercial	4/ 5′ to 4/ 3′
Precision	4/ 1′
High precision	4/ 30″ or tighter

Typical shop practice, not values from the standard verify. ISO 10110-6:2025 (3rd edition, “Centring and tilt tolerances”) is current verify.

Common mistakes

Leaving out the unit: 4/ 3 is ambiguous. Write 4/ 3′.
Not showing a datum. Without one, the datum axis is typically the axis of the outer cylinder (edge).
Specifying only tilt for an asphere. Add the lateral displacement L.

Questions

What does 4/ 3′ mean?

The surface may be tilted at most 3 arcminutes relative to the datum axis (ISO 10110-6).

How do I specify centring for an asphere?

Add the lateral displacement: 4/σ(L), for example 4/ 2′ (0.01) means 2 arcmin tilt and 0.01 mm decentre of the aspheric axis.

Sources

ISO 10110-6:2015 (public preview); ISO 10110-6:2025 catalogue entry. Full list and edition status: Sources & editions.

An unofficial summary written from public previews of the standards and reputable secondary sources. It does not reproduce the ISO text. Items marked verify could not be fully confirmed. Check against the current edition; see Sources & editions.