In general, we retain tolerances in the validation of drawings and production. Because there are uncertainties in the process, it is necessary to understand the dimensional tolerances.
Dimensional tolerance means that there is always a certain error in the actual size after completion due to factors such as machining or measurement during the manufacturing process of the part. In order to ensure the interchangeability of the parts, the actual size of the parts must be controlled within the allowable range of variation. This allowed amount of dimensional change is called the dimensional tolerance.