Dimensional tolerances specify allowed variability around nominal dimensions. We assign tolerances to assure component interchangeability while meeting performance and producibility requirements. In general, as tolerances become smaller, manufacturing costs become greater.

The tolerance assignment approach used by most organizations offers opportunities to reduce cost and improve quality through tolerance relaxation. While quality improvement based on relaxed tolerances seems counterintuitive, a quick look at how tolerances are assigned and the consequences of overly-stringent tolerances reveal why this is so.

To better define a part, Geometric Dimensioning and Tolerancing (GD&T) is often used as a symbolic way of showing specific tolerances on drawings. GD&T is a valuable tool that effectively communicates the design intent to manufacturing and inspection.

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