Class 3, is similar to Class 1A except it develops a thinner “conversion” layer.  Because the layer is thinner, it provides less resistance (than Class 1A) to electrical conductivity and therefore is preferred where electrical conductivity is needed after the conversion coating is applied.  Because Class 3 coatings are thinner, they are more susceptible to corrosion than Class 1A coatings. Class 3 coatings will also improve paint adhesion.