GB/T 1801-1999

This standard provides the foundational system for selecting tolerance zones and fits in mechanical engineering, defining the limits of size for holes and shafts to ensure interchangeable assembly. It is applied in the design and manufacturing of precision mechanical components, such as automotive parts, machine tools, and industrial equipment, where consistent fit (clearance, transition, or interference) is required. Engineers use it to specify dimensional tolerances on technical drawings and to guide quality control during production and inspection.