Our factory produces a series of internal thread parts in large quantities. The thread has a screw length of 20mm or more and requires 100% inspection. When the parts are machined with internal threads on the lathe, it is necessary to measure the threaded plug gauges several times, which consumes a lot of manpower and material resources. We designed and manufactured an internal thread measuring instrument (see figure) for this purpose, which works well. 1. The main body 1 of the internal thread measuring instrument has a keyway which is symmetrical with the axis of the main body 1. For the purpose of grinding, the keyway can be