(a–zc) are used for external features ( shafts ).
Indicates the position of the tolerance zone relative to the nominal (basic) size. iso 286 pdf
This part defines the basic terminology, symbols, and principles of the system, including the concepts of clearance, interference, and transition fits. (a–zc) are used for external features ( shafts )
(A–ZC) are used for internal features ( holes ). and principles of the system