Engineering tolerance

With a normal distribution, the tails of measured values may extend well beyond plus and minus three standard deviations from the process average.

The choice of tolerances is also affected by the intended statistical sampling plan and its characteristics such as the Acceptable Quality Level.

This relates to the question of whether tolerances must be extremely rigid (high confidence in 100% conformance) or whether some small percentage of being out-of-tolerance may sometimes be acceptable.

Genichi Taguchi and others have suggested that traditional two-sided tolerancing is analogous to "goal posts" in a football game: It implies that all data within those tolerances are equally acceptable.

Research and development work conducted by M. Pillet and colleagues[1] at the Savoy University has resulted in industry-specific adoption.

Dimensional tolerance is related to, but different from fit in mechanical engineering, which is a designed-in clearance or interference between two parts.

This would provide a clearance fit of somewhere between 0.04 mm (largest shaft paired with the smallest hole, called the Maximum Material Condition - MMC) and 0.112 mm (smallest shaft paired with the largest hole, Least Material Condition - LMC).

Many commercially available resistors and capacitors of standard types, and some small inductors, are often marked with coloured bands to indicate their value and the tolerance.

Low tolerance means only a small deviation from the components given value, when new, under normal operating conditions and at room temperature.

In civil engineering, clearance refers to the difference between the loading gauge and the structure gauge in the case of railroad cars or trams, or the difference between the size of any vehicle and the width/height of doors, the width/height of an overpass or the diameter of a tunnel as well as the air draft under a bridge, the width of a lock or diameter of a tunnel in the case of watercraft.