Need help to understand mechanical drawing for footprint
The datasheet describes a family of devices, which have similar shapes (disk with radial leads) but different dimensions.  The case sizes are identified by the nominal diameter (even though a 7mm part can actually be as large as 9mm). 



To avoid making an individual drawing for each size, the authors of the datasheet made one parametrized drawing with letter designators, and listed the mechanical dimensions in the table below.

So for instance, the diameter of the pin is marked as Øb on the drawing.  From the table we find that for 7mm size, will have pin diameter between 0.585mm and 0.685mm.


(p.10 in the datasheet)