Manufacturers do not need to over-engineer tolerances; they can select the most cost-effective fit that satisfies the functional requirement.
Represented by a letter, the fundamental deviation determines the position of the tolerance zone relative to the nominal size line (the zero line). use uppercase letters ( A to ZC ). Shafts use lowercase letters ( a to zc ). iso 286 pdf
The limits are -9 µm / -25 µm (Actual size must be between 49.975 mm and 49.991 mm). Hole-Basis vs. Shaft-Basis Systems Manufacturers do not need to over-engineer tolerances; they
The ISO 286 standard is not an island. It exists within a broader ecosystem of national and international standards. iso 286 pdf