Perfect flatness is that condition which exists when all points on a surface lie in the same plane.

Flatness tolerance is the permissible distance between two parallel planes within which all irregularities of a given surface must lie.

Parts may be measured in either unrestrained or restrained conditions. (Recommended limits are applicable to parts measured in the unrestrained condition.)

Bottom surface irregularities are illustrated.

Commonly used flatness tolerances for metal stamping are shown below.

Surface Length - Flatness Tolerances
From 0" to 1" - .005" T.I.R.
1" to 4" - .005/inch T.I.R.
Over 4" - .020" plus or minus .004/inch of additional length, T.I.R.

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