, the inner diameter, 
, length, 
. The magnetic reluctance is determined by:The axial cylinder models is characterized by the outer diameter, , the inner diameter, , length, . The magnetic reluctance is determined by:
The area of cross section yields:
A hollow cylinder is depicted in the above figure left for 
. A solid cylindric flux tube an be considered by setting the inner radius, , equal to zero.
A circular sector of the area of cross section with central angle 
is depicted in the above figure right.