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GD&T Rules

Here are some of the fundamental rules of geometric dimensioning and tolerancing per ANSI Y14.5:

  • All dimensions must have a tolerance.
  • Dimensions and tolerances shall completely define the nominal (ideal) geometry and allowable variation.
  • Dimensions and tolerances are valid at 20 deg C unless stated otherwise.
  • Dimensions and tolerances are valid when the item is in a free state unless stated otherwise.
  • Dimensions and tolerances apply to the full length, width, and depth of a feature.
  • Dimensions and tolerances only apply at the level of the drawing where they are specified.
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