This issue is a revision of ASME Y14.5-2009, Dimensioning and Tolerancing. The objectives for this revision are to
correct any inconsistencies in the previous edition, to determine actions based on deferred comments from the review of
the previous edition’s draft, to include model-based applications in many of the example figures, and to address proposals
submitted by the public or members of the Subcommittee. Based on guidance from the Y14 Committee, the material
formerly in Section 1 has been reorganized into Sections 1 through 4, and the subsequent Sections have been renumbered.
Because of the widespread use of computer-aided design (CAD) and the industry transition toward reduced use of
orthographic views for product definition, model views were added in many figures throughout the Standard. This is in
part to ensure that this Standard is applicable to the use of dimensions and tolerances in models and model-based
drawings. The methods of application in model views are currently defined in ASME Y14.41, but the meanings of
the tolerances are defined in this Standard.

The Foreword of ASME Y14.5-2009 pointed out the increasing importance for design to more precisely state functional
requirements through the use of geometric dimensioning and tolerancing (GD&T), and not to rely on the less definitive
method of directly applied limit dimensions for form, orientation, location, and profile of part features. This 2018 revision
emphasizes the use of profile for location tolerances applied to surfaces; the use of plus and minus tolerances has been
moved to an Appendix that is likely to be removed in the next revision.
With a focus on making the transition from the previous edition to this edition simple, no reversals of tolerancing
concepts have been made. However, two past practices, use of concentricity and use of symmetry symbols, are no longer
supported. Both have been eliminated because other characteristics provide more direct control of features and establish
requirements that have a well-defined meaning. Deletion of the symbols does not leave industry without a means to
control coaxial or symmetrical features, but it does eliminate the confusion that surrounds these symbols and their
misapplication.

Text and figure edits were made to improve readability and clarify content. Changes in sentence structure, organization
of content, and method of illustration are not an indication of technical changes.
Work on this issue began at a meeting in Sarasota, Florida, in April 2009. Numerous deferred comments from the public
review for the previous revision, as well as new proposals for revision and improvement from the Subcommittee and
interested parties in the user community, were evaluated at subsequent semiannual meetings. The first draft entered the
review process after it was completed in August 2015. Additional technical improvements and numerous editorial
changes were made based on the comments received.

A Nonmandatory Appendix provides information about many of the updates in this edition of this Standard. One of the
updates is an explicit statement that unless otherwise specified by drawing/model note or reference to a separate
document, the as-designed dimension value does not establish a functional or manufacturing target. In addition,
the term “true geometric counterpart” has replaced the term “theoretical datum feature simulator.” The use of the
“true geometric counterpart” term is limited to datums.

This Standard is available for public review on a continuing basis. This provides an opportunity for additional publicreview
input from industry, academia, regulatory agencies, and the public-at-large.
This revision was approved as an American National Standard on August 13, 2018.