GD & T

What Is GD&T?

GD&T is a symbolic language. It is used to specify the size, shape, form, orientation, and location of features on a part. Features tolerance with GD&T reflect the actual relationship between mating parts. Drawings with properly applied Geometric tolerance provide the best opportunity for uniform interpretation and cost-effective assembly. GD&T was created to insure the proper assembly

Of mating parts, to improve quality, and to reduce cost.

GD&T is a design tool. Before designers can properly apply geometric tolerance, they must carefully consider the fit and function of each feature of every part. GD&T, in effect, serves as a checklist to remind the designers to consider all aspects of each feature. Properly applied geometric tolerance insures that every part will assemble every time. Geometric tolerance allows the designers to specify the maximum available tolerance and, consequently, design the most economical parts.

GD&T communicates design intent. This tolerance scheme identifies all Applicable datum’s, which are reference surfaces, and the features being controlled to these datum’s. A properly tolerance drawing is not only a picture that communicates the size and shape of the part, but it also tells a story that Explains the tolerance relationships between features.

GD&T Symbol	Control Type	Name	Summary Description
	Form	Straightness	Controls the straightness of a feature in relation to its own perfect form
	Form	Flatness	Controls the flatness of a surface in relation to its own perfect form
	Form	Circularity	Controls the form of a revolved surface in relation to its own perfect form by independent cross sections
	Form	Cylindricity	Like circularity, but applies simultaneously to entire surface
	Profile	Profile of a Surface	Controls size and form of a feature. In addition it controls the location and orientation when a datum reference frame is used.
	Profile	Profile of a Line	Similar to profile of a surface, applies to cross sections of a feature
	Orientation	Perpendicularity	Controls the orientation of a feature which is nominally perpendicular to the primary datum of its datum reference frame
	Orientation	Angularity	Controls orientation of a feature at a specific angle in relation to the primary datum of its datum reference frame
	Orientation	Parallelism	Controls orientation of a feature which is nominally parallel to the primary datum of its datum reference frame
	Location	Position	Controls the location and orientation of a feature in relation to its datum reference frame
	Location	Concentricity	Controls concentricity of a surface of revolution to a central datum
	Location	Symmetry	Controls the symmetry of two surfaces about a central datum
	Runout	Circular runout	Controls circularity and coaxiality of each circular segment of a surface independently about a coaxial datum
	Runout	Total runout	Controls circularity, straightness, coaxiiality, and taper of a cylindrical surface about a coaxial datum