When mechanical drawings or CAD models include a note such as “DIMENSIONING AND TOLERANCING PER ASME Y14.5-2018” we should expect to find properly applied, part function-driven GD&T based on the requirements of the ASME Y14.5 standard. Y14.5 defines GD&T methods to define tolerance zones that may be constrained to a datum reference frame, with a requirement that a defined feature element must be inside the tolerance zone for each specification.
When GD&T is applied well, the datum reference frame, tolerance zones, controlled feature elements, and the numerical values that specify the allowable imperfection in the size, form, orientation, and location of part features will directly address the functional requirements of the part. The objective of GD&T specifications is to provide the means to predict whether a part will function or not, based on the measurement data reported for each tolerance specification. A secondary objective is to provide meaningful additional data that helps design and manufacturing teams better understand how their design or their processes are performing.