The gage consists of an eccentric inner wheel, supported by two larger outer concentric wheels. At a specific point, the inner wheel touches and picks up wet film when the gage is rolled on the coated surface. This critical clearance may be read on a rotating scale.
The gages may be held between the thumb and forefinger to take a reading, or it may be inserted into the gage holder. This holder is widely used to measure coatings safely on moving surfaces such as high-speed press rollers. It can also be used on stationary, flat, or curved surfaces since the holder makes it easier to exert a steady, even force on the gage.