GEOMETRIC TOLERANCING AND DIMENSIONING
Geometric dimensioning and tolerancing (GD&T) is an accurate technique for defining and controlling the forms and shapes of features. Its unique approach in dimensioning is the independent specification of the size and geometric tolerances. It combines general and geometric tolerances in a feature control frame. Geometric tolerance types include straightness, flatness, circularity, and cylindricity, and orientations of shapes such as angularity, parallelism, and perpendicularity. Run-out relates to radial features and reference axis and features that are 90o to a reference axis. Table A3.1 shows the commonly used geometric tolerancing symbols that are adopted internationally. Figure A3.1 shows examples of GD&T.
Table A3.1. GD&T symbols
