Measuring device for measuring inner diameter tolerance of circular ring body

A measuring device for measuring an inner diameter tolerance of a circular ring body comprises a measuring instrument (5), a first locating ball (1), a locating sleeve (2), a pressure spring (3), a cover plate (4), a measuring rod (6), a balancing frame (7), a second locating ball (8), a limiting sleeve (9) and a radially moving locating ball (10), wherein a spacing between centers of the first locating ball and the second locating ball which are fixed at two ends of the balancing frame is C, the minimum point of the radially moving locating ball which is fixed by the measuring rod and the limiting sleeve along a middle point of the balancing frame, and a line between the minimum points of the first locating ball and the second locating ball can form a height difference h, then the radius r of the circular ring body can be obtained according to the formula h = r - 1/2 ( 4r - C ) . The measuring instrument is connected with the measuring rod through the cover plate, the locating sleeve and the pressure spring, and the difference of absolute values of a measured value read by the measuring instrument and an original value is the tolerance of the inner diameter 2r of the circular ring body. The measuring device of the utility model has the advantages of simple structure, portability, and convenient and fast measurement.