The ornamental design for a hub of an axialfan, as shown and described.
FIG. 1 is a perspective view of a hub of an axial fan, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a left-side view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken line showing of fan blades and a portion of a fan is included for the purpose of illustrating environmental structure and forms no part of the claimed design.