Measuring Thickness

Other Hardware Sensors
1

I want to make a device for measuring thickness in micrometers of paint applied to steel, which sensor could I use in a project like this?
Help me please

2

there are ready made Paint Thickness Gauges. See principles here

you can probably find some of those devices with a serial or rs232 output

3

Examples of commercial units:
paint thickness gauge for car - Buy paint thickness gauge for car with free shipping on AliExpress

Not a recommendation of purchase. With specialty sensors, it is often less expensive to purchase a commercially constructed product.