In production practice, we have found that in the hole system of the box-like parts, the positional size between the light holes is generally stable unless the glue plate and the power head fail. However, the position between the optical hole and the threaded hole and the threaded hole is often not stable. To measure the same size of the three-dimensional part that is continuously processed, there is often a phenomenon in which one part is out of tolerance and the other part is qualified. The position size is again shown to be acceptable. This has caused great difficulties for the production department and the maintenance department.