ISO 8674:2012 specifies the characteristics of hexagon high nuts (style 2) with metric fine pitch thread, with nominal thread diameters from 8 mm up to and including 36 mm, with product grade A for sizes D ≤ 16 mm and product grade B for sizes D > 16 mm.
Coarse thread hexagon nuts, style 2, according to ISO 4033 are intended to be the first choice.