Pre load specification

How are ground pre-loaded bearings ordered/specified? Is the preload
specified in thousands of an inch (or similar)? I believe Ballendo
said they could be ordered from the manufacturer pre-ground, is this
what is typically done, or is the preload accomplished by the end
user? Finally, how is the preload inspected? For instance, since the
torque on the lead screw nut affects the final preload (as I
understand it), how is the nut torque chosen? How does this torque
relate to the final pre-load?

Thanks in advance,

Ron