Abstract: A pneumatic sensor head for monitoring the thickness of a continuously moving sheet of material passing therethrough. The sensor head is comprised of first and second blocks having respective first and second aligned nozzles separated by a distance sufficient to receive the sheet of material passing therethrough. The sensor head is further comprised of means for admitting pressurized fluid to the first and second nozzles to sense an average variation in the back pressure therefrom proportional to a change in the thickness of the sheet material being monitored. A plurality of removable stacked laminated sheets is positioned between the first and second blocks for adjusting the distance between the first and second nozzle, whereby to enable operation of the sensor head over wide variations in nominal thickness of monitored sheets of material.