Most quality technicians have been exposed to and probably use geometric dimensioning and tolerance (GD&T) information in their day-to-day work duties. After all, GD&T has been in use for over 50 years. The creation of it is credited to Stanley Parker who developed the notion of “true position.” GD&T more accurately defines the features of a part using a variety of standardized symbols. The “language” of GD&T has four core elements: size, form, location, and orientation. There are an additional ten primary feature control symbols that round out the GD&T language. The total 14 are:
On a part drawing, the appropriate GD&T symbols are included, along with the numerical dimension and tolerance for each feature, all of which are usually placed within a frame. For those unfamiliar with reading drawings, these “feature frames” look like they contain secret codes. Additional frames are connected if there is more than one “message” needed for a particular feature. The GD&T code contains pertinent information to be sure!