screw diameter

They simply refer to the size of the threads relative to the screw diameter.

The diameters of the nut and rollers (7 - 14 in quantity) are simple functions of the screw diameter and lead.

For a given screw diameter and quantity of thread starts more rollers corresponds to higher static load capacity, but not necessarily to a higher dynamic load capacity.

Coarse threads have a larger threadform relative to screw diameter, whereas fine threads have a smaller threadform relative to screw diameter.