Zinc plating is identical to electro-galvanizing in principle because both are electro-deposition processes. However, zinc plating is used on small parts such as fasteners, crank handles, springs and other hardware items rather than sheet metal. The zinc is applied as an expendable electrode in a cy, alkaline non-cyanide, or acid chloride salt solution
The normal zinc-plated coating is dull gray in color with a matte finish, although whiter, more lustrous coatings can be produced, depending on the process or agents added to the plating bath or through post-treatments. The coating is thin, ranging up to 1 mil (25 µm), restricting zinc-plated parts to very mild (indoor) exposures. ASTM Specification B 633 lists four classes of zinc plating: Fe/Zn 5, Fe/Zn 8, Fe/Zn 12 and Fe/Zn 25. The number indicates the coating thickness in microns (µm). The coating finds application in screws and other light fasteners, light switch plates and other small parts. Materials for use in moderate or severe applications must be chromate conversion coated. The coating is entirely pure zinc, which has a hardness about one-third to one-half that of most steels.
The most common standard for zinc plating is ASTM B633, which has four classifications for electroplated zinc. Each classification specifies which supplemental treatment or chromate to apply (Type I,II,III,IV,V, or VI) and the plating thickness according to the type of environment (SC1, SC2, SC3 or SC4)