How do GD&T tolerances communicate functional fit that would be difficult with linear dimensions?

How do GD&T tolerances communicate functional fit that would be difficult with linear dimensions?

• A. They express allowable geometric deviations with datums and tolerance zones, clarifying function and interchangeability
• B. They use color codes
• C. They ignore datums
• D. They specify only size

Answer: (A)

GD&T tolerances communicate functional fit by tying how a feature must relate to the rest of the part and to mating parts to a defined reference frame. Datums establish that frame, and tolerance zones specify the permissible deviation for form, orientation, location, and runout. This lets you state, for example, that a hole must lie within a cylindrical tolerance zone at a certain position relative to datums, so a mating pin will insert reliably and parts interchangeably fit together even with manufacturing variation. Linear dimensions alone set size but don’t control where a feature sits or how it is oriented, so two parts can be the same size yet fail to assemble correctly. Hence GD&T communicates function and interchangeability through tolerances that reference datums and defined zones, beyond what size alone can express.

GD&T tolerances communicate functional fit by tying how a feature must relate to the rest of the part and to mating parts to a defined reference frame. Datums establish that frame, and tolerance zones specify the permissible deviation for form, orientation, location, and runout. This lets you state, for example, that a hole must lie within a cylindrical tolerance zone at a certain position relative to datums, so a mating pin will insert reliably and parts interchangeably fit together even with manufacturing variation. Linear dimensions alone set size but don’t control where a feature sits or how it is oriented, so two parts can be the same size yet fail to assemble correctly. Hence GD&T communicates function and interchangeability through tolerances that reference datums and defined zones, beyond what size alone can express.