A fluid-cooled x-ray tube has a closed coolant circuit in which coolant circulates for the elimination of the generated heat. The slider is exfoliated from the suspension in the state that the one joint member is attached to the slider by heating and melting the other joint member. The apparatus can be used to characterize various aspects of the threaded surface, including generating the measurements required to produce a longitudinal cross-sectional profile of the threaded surface. In consequence, a calculation amount can be decreased to increase a calculation speed as compared with conventional CG04, FI05 and DP06 systems.