Abstract: An apparatus is disclosed for checking the geometric characteristics of mechanical objects having rotational symmetry, such as shafts or bushings. A longitudinal support element defines a longitudinal axis and first reference surfaces, at least one modular coupling element is removably coupled to, and is adjustable longitudinally along, the longitudinal support element and provides second reference surfaces which cooperate with the first reference surfaces to align a linear guide portion transversely of the longitudinal axis. A fastener secures the modular coupling element, which removably supports a gauging device, to the longitudinal support element and a locking/unlocking device cooperates with the gauging device and guide portion for locking the gauging device to the modular coupling element.