Cylinder gauge is a comparison measuring device for measuring the inner diameter of the hole by comparison with a master gauge (micrometer ring gauge, etc.). The guide plate guides the center of the gauge head and conversion rod diameter portion of the bore (automatic centering mechanism), convey a displacement of the probe perpendicular converted dial gauge in one-to-one by the cam mechanism, reads the displacement of the dial gauge . The measurement accuracy varies depending on scale interval (resolution) of the dial gauge to be used. We offer a measurable lineup up to φ450mm from the minimum φ6mm depending on the size of the inner diameter.