mikrometry
https://www.mikrometry.com/products/etg12f1-magnetic-coating-thickness-gauge.html
The magnetic coating thickness gauge ETG12F1 is a professional tool and at the same time easy-to-use device that is used for accurate measurements of coatings or coatings on various metal surfaces. High dust, gas pollution, changes in humidity and temperature will not stop the operation of this magnetic film thickness gauge device. This magnetic paint thickness gauge machine is designed to not-destructively measure the thickness of non-magnetic coatings(including paint, enamel, plastic, epoxy, etc)on iron or steel.
The measuring paint thickness on metal is mainly measured and determined based on this pulling force. Thinner coatings generally have greater magnetic attraction, while thicker film coatings have relatively less magnetic attraction. The pull off paint thickness gauge magnetic type is very sensitive to measuring the surface roughness, curvature, substrate thickness and composition of metal alloys of samples.