Definitions:
Nominal Diameter of Rivet (dn)
That is the diameter of the shank of the rivet before driving.
Gross Diameter of the Rivet (d)
That is the diameter of the rivet hole, that is given by the following equation.
d = dn +1.5 mm, for dn ≤ 25 mm
d = dn + 2.0 mm, for dn > 25 mm
It is supposed that the shank of the original rivet during driving will expand and, thus, completely fill up the slightly larger area of the rivet hole.