Abstract: In order to make better use of the definition local size for the design of mechanical
tolerance under current tolerance standards. The concepts of local size in ASME Y14.5 and ISO/GPS
were introduced. The differences in the use of local size in ASME Y14.5 and ISO/GPS were analyzed
with the application of local size in an automatic feeding mechanism. The two tolerance standards
differ in setting the local size, using tolerance principle and adding symbols to realize geometrical
functions. Then, the geometrical specifications of the motor shaft were analyzed when using
two-point measurement methods can’t detect the local size. The geometric tolerances items were used
to replace the dimensioning of sector-cylinder to avoid the detection of local size. It is of positive
significance to correctly understand the concept of the local size, relevant symbols and its detection
characteristics, and to avoid ambiguous dimensioning, which can guarantee the functionality and
assemblability of parts, and can improve the economy.

Key words: local size, geometrical product specification, geometrical dimension and tolerance;
tolerance principle, surface profile