For fittings that have been properly cleaned, it is impossible to determine the method of cleaning or passivation that was used. This film results from a continual process of low-level oxidation, so oxygen from the atmosphere is needed for the passive film to exist. Once formed, it prevents further oxidation or corrosion from occurring. Even if chipped or scratched, a new passive film on stainless will form. Removing surface impurities by using chemicals.
Pitting indicates deep corrosion in localized spots on a fastener.
Dirt or grease on certain portions of a fastener may block oxygen from that surface, thus impeding the passsive film that protects stainless from corrosion. A test load that a fitting must undergo without showing significant deformation. Class 1 threads are a loose tolerance. Class 3 threads have a stricter tolerance and tighter fit such as socket cap and set screws. No definite relationship exists between tensile strength and tightness or looseness of fit.