Hollow spindle with a inner bolt and nut set is not widely used. Normally it is for plastic handles or small handles when a hex fixing screw can not be applied.
Plain handle spindle is the most popular type used.The spindle passes through the door and locates into the square hole in the rear of door handle.
Spindle with Inner Bolt
A hex nut screw head spindle is a type modify from plain spindle. The hex nut screw part can rotating freely, so the with hex nut screw fixed handle can not open the door.