General Tolerances: Symmetry

Symmetry is included in the general tolerances specified in ISO 2768-2:1989. It defines how accurately a part’s centerline or median surface must be positioned in relation to opposing surfaces or features when no separate tolerance is specified.

General tolerances ensure that asymmetry remains within controlled limits and that parts function as intended, for example in rotating components, joints, and aesthetically visible structures. At the same time, they prevent unnecessarily tight tolerances from being specified, which facilitates manufacturing and reduces costs.

As with other general tolerances, symmetry does not need to be indicated separately on the drawing; a designation such as ISO 2768-mK is sufficient. This indicates that the permissible deviations specified by the standard also apply to symmetry.

General Tolerance Table: Symmetry

Tolerance class	Straightness and flatness tolerances for nominal length ranges
Designation	>		100	300	1000
	≤	100	300	1000	3000
H		0.5	0.5	0.5	0.5
K		0.6	0.6	0.8	1
L		0.6	1	1.5	2

The values in the table are given in millimeters (mm).