This document specifies the procedure for determining the resistance of an organic coating on a metallic substrate to penetration by scratching with a needle.
It is possible that with some aluminium alloys and thin gauge steel substrate below 0,4 mm, that rather than scratching, the needle will deform the substrate. Under these conditions, this test method is not applicable.
Soft coatings such as poly vinyl chloride (PVC) and structured coatings will not give a precise result due to the soft nature of the coating and/or the potential for the needle to snag.
The method is not applicable to conductive coatings.