General rules

The symbols relating to geometrical characteristics are shown in Fig. 20.1 with additional symbols used in tolerancing in Fig. 20.1A. Examination of the various terms - flatness, straightness, concentricity, etc. - used to describe the geometrical characteristics shows that one type of geometrical tolerance can control another form of geometrical error.

For example, a positional tolerance can control perpendicularity and straightness; parallelism, perpendicularity, and angularity tolerances can control flatness.

The use of geometrical tolerances does not involve or imply any particular method of manufacture or inspection. Geometrical tolerances shown in this book, in keeping with international conventions, must be met regardless of feature size unless modified by one of the following conditions:

(a) Maximum material condition, denoted by the symbol @ describes a part, which contains the maximum amount of material, i.e. the minimum size hole or the maximum size shaft.

(b) Least material condition, denoted by the symbol (L) describes a part, which contains the minimum amount of material, i.e. the maximum size hole or the minimum size shaft.

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