Abstract
The coming to practical use of the symmetrical arc tooth gear starts in 1964. Atfirst, it used for gradually the heavy load from the light load. At present, it is used for the use field of the Involute gear which this geae quenched in the carbonization, too. The machine of this gear increase and the deceleration has about 5000 results. It reports on the process of this coming to practical use, and the followup surver, it introduces about the record article of the actual device and so on, too. In the actual device, it had encountered to the product accident, evaluating the strength of the symmetrical arc tooth gear, being surplus, too. It reports these experieces as much as possible using the figure and the photograph.
