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Know which Rules Apply to the Drawing
(In accordance with the ASME Y14.5-2009 standard)

PDF of this Tip

The rules of geometric dimensioning and tolerancing have changed over the years. In addition, the meaning of such symbols as runout, total runout, concentricity and symmetry have changed. You cannot go by the drawing date since many companies may delay adoption of a new revision for several years. Unfortunately, the drawing doesn’t always state the revision to use when translating the symbols into plain English. Often you can determine which Standard was used by observing differences in the callouts. Your choices of Y14.5 standard revisions are 1966, 1973, 1982, 1994 and 2009. Here are a few things to look for when determining which revision of the Standard to use. Reasons for these revisions include trying to be compatible with ISO standards, changes in technology and the increasing complexity of new products.

The Committee did a nice job of not making drastic changes to the appearance and meaning of geometric tolerancing when the 2009 revision came out.  Some new symbols were added as was a great deal of clarification.  The symbols that were added in 2009 are shown in this chart.

You still should always look for a note stating which revision of the Standard to use when reading the drawing.

Back to Tips Tip added Dec 2011