What is the difference of Type I, Type II and Type III Anodizing?

Just to clarify to anyone who don't want to read the thick ISO standard and just want to know some common sense on this.

Type I = chromic anodize, very thin, not usually dyed, used when sulfuric might be trapped in the part and in other specialized circumstances.

Type II = sulfuric anodize to a minimum of 1000 mg per square foot. Class 1 is not dyed, class 2 is dyed. Both are sealed to increase corrosion resistance.

Type III = sulfuric anodize done at a much lower temperature and higher current density than Type II to give a thicker and denser coating that has more abrasion resistance. The abrasion resistance will be reduced by sealing, so this coating is not normally sealed, although it can be.

Leaving out Type I, Type II is most preferable when cosmetics are important, Type III is most preferable when the extra abrasion resistance is needed.

And, ahh, More interest? Come back to thick ISO book... or click here to WiKi.