General and Geometric Tolerances

A general tolerance is usually given for all dimensions on a drawing. An individual tolerance may be given to a dimension where general tolerances are inadequate or restrictive. Tolerances may be expressed by quoting the upper and lower limits, the nominal dimension or the limits of tolerance above and below that dimension.

Geometric tolerances are used, where it is sometimes necessary to place tolerances both on geometric features and dimensions, in order to control the shape of a part adequately. A recommended system can be found in the BS 308. This is information usually required during manufacture.