3.1 Symbols

The symbols for the drawing indications of geometrical tolerances according to ISO 1101, ISO 5459, ISO 286 and ISO 10579 are shown in Tables 3.1 and 3.2.

Table 3.1: Symbols for geometrical tolerancing (see also 21)

Symbol	Interpretation
	Envelope requirement
	Maximum material requirement
	Least material requirement
	Reciprocity requirement
	Projected tolerance zone
	Flexible part in free state
	Regardless of feature size (ASME Y14.5)
	Tangent method (ASME Y14.5)
	Unsymmetrical tolerance zone (ASME Y14.8)
MD	Applies to major diameter of threads, splines, gears
PD	Applies to pitch diameter of threads, splines, gears
LD	Applies to (least) minor diameter of threads, splines, gears
LE	Applies to line elements (section lines)
NC	Not convex
ACS	Any cross-section
Further symbols are planned according to ISO 14 405 (in preparation)

Table 3.2: Geometrical tolerances and tolerance symbols

Table 3.2 shows the symbols for the geometrical tolerance characteristics.

With the symbols of the left column of Table 3.2 all kinds of geometrical tolerances can be expressed. The symbols of the right column cover special cases that occur very frequently. These symbols are standardized in addition, and should be used in order to facilitate readability of drawings.

The proportions of the symbols for the drawing indications are standardized in ISO 7083. However, some CAD systems deviate from this standard. This may be tolerable as long as the drawing indications are unambiguous (as demonstrated in this book).

3.2 Definitions of geometrical tolerances

In order to specify geometrical tolerances, the workpiece is considered to be composed of features (geometrical...