10 Geometric Dimensioning and Tolerancing Copyright Goodheart-Willcox Co., Inc. production, including designers, manufacturers, and inspectors. GD&T is necessary for any production level product and allows the personnel involved to accomplish the following: • Confirm components in an assembly fit together and are interchangeable. • Make sure that defective parts are rejected and quality parts are accepted. • Improve the design and quality of a product. • Reduce design revisions. • Lower design, manufacturing, and inspection costs. • Verify the design and functional relationships of parts. • Outsource design and production work to subcontractors. Comparing directly toleranced coordinate dimensioning to geometric tolerancing provides the basic foundation to understanding why GD&T is important. A directly toleranced dimension is a dimension with an associated plus and minus (±) toler- ance or limit dimension values. Coordinate tolerancing refers to the use of coordinate dimensioning with directly toleranced dimensions. Coordinate tolerancing uses the rectangular coordinate system to locate the features of a part. In this system, dimen- sions specify linear distances from the X, Y, and Z axes. Example 1-5 shows a metric unit drawing of a face plate dimensioned using coordinate tolerancing. Notice that plus and minus tolerances are directly applied to the dimensions. Drafting, design, and training for all disciplines. ENGINEERING DRAFTING & DESIGN, INC. Integrity - Quality - Style Goodheart-Willcox Publisher Example 1-5. A metric unit drawing of a face plate defined using coordinate tolerancing. The linear dimensions are directly toleranced rectangular coordinate dimensions.