MEASURING APPARATUS

PURPOSE:To measure a plane which is orthogonal to the central axial line of a tapered part readily by providing a master gate wherein the inner surface or the outer surface of a tapered part is accurately formed, and providing an indicator having a probe which is extending in the radial direction with respect to the central line of the tapered part in parallel with said central line. CONSTITUTION:When a tool holder 12 of a machine tool is machined, a block gage is mounted on a gage line 3 of a master gage 1 beforehand. The tip of a probe 10 of each electric micrometer head 6 is brought into contact with the block gage. The indicated scale value of a display at this time is set at zero. A tapered shaft 12a of the tool holder 12 which is machined slightly thickly is inserted into a tapered hole 2 of the master gage 1. The probe 10 of the electric micrometer head 6 is brought into contact with a side surface of a flange part 13 of the tool holder 12. The measured value of a display 11 is read. The tapered surface of the tapered shaft 12a and the side surface 13a of the flange part are ground so that the measured value of each indisplay 11 becomes zero.