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Toleranced Dimensions Still Have Their Place
(In accordance with Y14.5M-1994 standard)

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Many companies are using a general profile of a surface tolerance in place of the "old school" general plus/minus tolerance. As pointed out in earlier Tips, the advantages include:

Consequently, toleranced dimensions are being replaced by BASIC dimensions. Although this approach will be the standard practice in the future, toleranced dimensions still have a place on most drawings. If, for example, the general profile of a surface tolerance is relied upon to control wall thickness, large variation could result.

To reduce this variation, a general wall thickness with a tolerance may be used as a refinement of the general profile tolerance. In this example, with a general profile tolerance of 0.5 mm and a nominal basic wall of 0.5 mm, without a wall thickness note, the wall thickness could vary from 1 mm to zero.

The general wall thickness note as a refinement prevents this from happening. This wall thickness dimension is a local size that must be met at each cross section.

Back to Tips Tip added Jul 2001