The GD&T Guide
← Back to all symbols

Location control

Concentricity

What it controls

Concentricity controls the derived median points of a feature relative to a datum axis. It may be encountered on older drawings, but ASME Y14.5-2018 withdrew it in favor of more practical controls such as position or runout when appropriate. The derived median points of a cylindrical or spherical feature.

The tolerance zone

How the zone works

The derived median points of the controlled feature must lie within a cylindrical zone centered on the datum axis. This is not the same as requiring the actual surface to have low indicator reading during rotation.

Example drawing

See Concentricity on a drawing

Concentricity GD&T example drawing
Concentricity applied to derived median points relative to a datum axis

Tolerance zone visualized

See the tolerance zone in context

Concentricity illustrated as a cylindrical zone containing derived median points about datum axis A.

Why it is a specialized control

Concentricity controls the relationship of median points, which are constructed from opposed surface elements. That makes the requirement difficult to measure directly and often more restrictive than a design team intends. When the functional need is axis location or surface behavior during rotation, position or runout is usually a clearer choice.

Example feature control frame

Concentricity feature control frame showing a 0.20 diameter tolerance relative to datum A

The derived median points of the indicated diameter must remain inside a ⌀0.20 mm cylindrical zone coaxial with datum axis A.

Left cellThe geometric control.
Middle cellThe size and shape of the allowed zone.
Right cellsThe datum references establish the inspection setup.

Practical use

When to use Concentricity

Reserve concentricity for the rare situation where the distribution of material around a datum axis—not simply the location of an axis or the spinning surface—is the actual functional requirement.

Inspection

How it is usually measured

A CMM is the practical choice because it can collect opposed surface points and construct the median points. An indicator on a rotating diameter measures runout, not concentricity, so it cannot by itself prove this control.

Common mix-up

Concentricity does not directly control the surface itself and can be difficult to inspect. Check whether position or runout better reflects the actual functional need.

Keep exploring

Browse every symbol

Open the full library →
StraightnessFlatnessCircularityCylindricityProfile of a LineProfile of a SurfaceAngularityPerpendicularityParallelismPositionCircular RunoutTotal RunoutConcentricityCurrent pageSymmetry