A six-nozzle plug air gauge has been developed to measure diametral creep of tubular specimens of 23 mm internal diameter for distances up to 7.5 m within a nuclear reactor. The progressive changes made to the air gauging system to increase range, improve reproducibility and decrease response time are described. The present system can measure up to a difference of 0.65 mm between the diameters of the gauge head and that of the tube being measured.