Hard Anodizing produces superior resistance to abrasion and provides greater coating density.  It is similar to Sulfuric Acid Anodize (Type II) except it is typically applied at lower temperatures and at higher electrical current density, resulting in increased anodic growth.  Because hard anodize produces thicker depositions, it may be used to salvage components that are inadvertently over-machined (up to .003”) during manufacturing.  The anodic film produced is 1.5-2.5 MILS for most applications with a hardness of 65 Rockwell "C".  The application produces 50% penetration in the substrate and 50% growth over the original dimensions of the parts.  Hard Anodize strengthens the aluminum to a hardness of steel and provides higher wear properties and greater electrical resistance.   Coatings have heightened surface roughness and are softer on the top surface than down in the core of the coating.  Sealing of the coating reduces wear resistance & fatigue strength.  Sealing is only recommended when corrosion resistance is a factor.