Concentricity… or Co-axiality

Both concentricity and co-axiality share the same control feature symbol which can cause confusion.

Concentricity = 2D & Co-axiality = 3D

Concentricity is a 2D tolerance zone feature around a theoretically exact centre point of the datum. Typically used to control position of one circle to another, however as form is not considered, concentricity can be used on other shapes too

Co-axiality is a 3D tolerance zone a theoretically exact centre axis. Typically used to control one cylinder to another cylinder. However, like concentricity, form is not considered so other shapes can be considered.

In most cases where depth is considered i.e. a hole. Co-axiality should be used over concentricity

The concentric tolerance of 0.05mm and the final diameter 10.2/9.8mm must be treated separately. The concentric tolerance has no influence on the final diameter of the component. Instead it is the theoretical centre of the 10.2/9.8mm section that must lie within the 0.05mm tolerance zone stated.