... field conditions. * The F probes measure the thickness of non-magnetic materials (e.g. paint, plastic, porcelain enamel, copper, zinc, ... iron, nickel etc.) . often used to measure the thickness of galvanizing layer, lacquer layer, porcelain enamel layer, phosphide ... probes measure the thickness of nonmagnetic coating on magnetic metas . It is used on anodizing, varnish, paint, enamel,plastic coatings ...