Flatness

Related terms

GD&T

GD&T is geometric dimensioning and tolerancing, the symbol system defined in ASME Y14.5 and ISO 1101 for controlling the form, orientation, location, and runout of part features relative to datums. It states functional intent more precisely than plus-minus dimensions and often allows larger tolerances where they do not matter.

Tolerance

Tolerance is the total amount a dimension is allowed to vary from its nominal value, such as ±0.005 in (±0.13 mm). Tighter tolerances raise cost through slower processes, extra operations, and added inspection. Hold them only on features that affect fit or function.

Datum

A datum is a theoretically exact point, axis, or plane, established by a real feature on a part, from which other features are located and measured. Drawings list datums in order of precedence (primary, secondary, tertiary), which tells inspection how to fixture the part.