Concentricity refers to a center of circular surfaces if the diameter of a cylinder is smaller than its hight.
In this case, for example, the center of a hole must be inside a circle of the specified diameter.
This applies around a reference point in the cross section.
For coaxiality, the axis of a selected diameter must be within a tolerance zone, which is represented by a cylinder of given diameter.
The axis or directional normal must lie on a common reference axis A-B.
The rule that cylinders with diameters greater than their height are tolerated via concentricity serves to distinguish the two terms.
Otherwise, coaxiality is tolerated.
This glossary of plastic industry is provided by PLEXPERT Canada Inc.