Device for measuring runout of conical surface to pitch diameter of thread

A device for measuring run-out of the pitch diameter of a conical surface to a thread comprises a base, a shell, a positioning mandrel, a threaded ring, a support, a puller screw, a gasket and a dial indicator, when the device is used, a part to be measured is installed in a threaded hole of the threaded ring, and the tail of the positioning mandrel is in threaded connection with the gasket in a matched mode. During measurement, the head of the positioning mandrel abuts against an inner hole of a to-be-measured part, then the threaded ring is rotated by a circle, and the maximum swing value of the dial indicator abutting against the side wall of the threaded ring is read, namely, the runout value of the inner conical surface of the part to the pitch diameter of the thread. According to the invention, the thread pitch diameter of a small part is converted to the easy-to-detect excircle surface through the thread ring, and then the dial indicator is used for measuring the run-out value, so that the problem that