ISO 17668:2016 specifies minimum thickness requirements for six classes of zinc diffusion layers applied to ferrous products by the sherardizing process for the purpose of protection against corrosion and wear.ISO 17668:2016 does not specify any requirements for the surface condition (finish or roughness) of the basis material before sherardizing.Post-treatments (conversion coatings), after-treatments or organic over-coatings (Duplex) of sherardized articles are not in the scope of this International Standard.NOTE 1 For general information about post-treatments, see Annex C and Annex D.ISO 17668:2016 does not apply to sherardized products (e.g. fasteners, tubes) for which specific standards exist and which might include additional requirements or requirements which are different from those of this International Standard.NOTE 2 Individual product standards can incorporate this International Standard for the coating by quoting its number, or can incorporate it with modification specific to the product.