GD&T or geometric dimensioning and tolerancing, represents a way to define the size, location, orientation, and form of a part feature.
GD&T is a symbolic language on both engineering drawings and/or three-dimensional models to describe the “perfect” geometry of parts and assemblies and to determine the allowable variation in form or size of individual features, defining the amount of variation between the features. It removes ambiguity, communicating the permissible limits of imperfection in real-world machine parts:
- The designer conceives his design using CAD in an idealized perfect form
- Real manufacturing processes are not perfect and thus introduce variation to the real manufactured parts
- The designer needs to specify how much variation is allowed in the real parts in order to ensure proper assembly and functioning
- GD&T is the language for communicating these limits of variation on the form, size, orientation and location of part features