Copyright Goodheart-Willcox Co., Inc.
Preface 3
Preface Preface
A majority of commercial and military indus-
tries require their engineers, designers, and any-
one involved in creating design documentation
to be knowledgeable in proper dimensioning and
tolerancing methods. This knowledge is important
in product design, production equipment design,
and tooling design. People that work in the pro-
curement and manufacturing of parts are also
expected to understand dimensions and toler-
ances. Machinists, machine programming person-
nel, tool makers, inspectors, and manufacturing
engineers must understand dimensions and toler-
ances since they work to the specifi cations created
by the engineers and designers.
The guidelines for consistent and clear appli-
cation of dimensions and tolerances are defi ned
by national standards as written by the American
Society of Mechanical Engineers (ASME). The
number of companies requiring compliance with
national standards is continually growing. Stan-
dards written by the International Organization
for Standardization (ISO) also defi ne dimension-
ing and tolerancing requirements and are becom-
ing widely used. The ISO methods are similar to
ASME standards, but there are detailed differences.
Proper application of dimensions and toler-
ances is an important part of providing complete
documentation of product requirements. ASME
Y14.5 is the authoritative document for defi n-
ing dimensioning and tolerancing symbols and
application methods. ASME Y14.41 provides fur-
ther explanation specifi cally applicable to digi-
tal product defi nition (computer-aided design).
GD&T: Application and Interpretation provides an
expanded explanation of the material contained in
these and other applicable ASME standards. Addi-
tional standards that affect calculation and appli-
cation of tolerances are explained and referenced
within this text when appropriate.
The subject of this text ranges from the fun-
damentals of dimension application to extended
principles of tolerance application. It provides
introductory information on GD&T for an entry-
level class while also providing the informa-
tion needed for in-depth understanding and use
as a reference book in education and industry.
Although the importance of dimensioning funda-
mentals is reduced by the utilization of solid mod-
els to establish dimensional requirements, this
text provides an explanation of the fundamentals
since some companies still create fully dimen-
sioned product defi nition. Not everyone will need
to know the dimensioning fundamentals since
industry is transitioning away from the visible
display of dimensions and allowing the computer-
generated geometry to defi ne dimension values.
Tolerance application and interpretation expla-
nations in this textbook are included for all of the
categories of tolerances in ASME Y14.5. Explana-
tions are primarily based on the current version
of the standard, ASME Y14.5-2009. Past practices
as defi ned in earlier releases of ASME Y14.5 are
briefl y explained to provide information for peo-
ple who encounter tolerance specifi cations that
were created prior to issuance of the current stan-
dard. Past practices, where included in this text, are
clearly distinguished from current practices.
GD&T: Application and Interpretation contains
twelve chapters. A list of major topics is provided
at the beginning of the chapter. A chapter sum-
mary is given at the end. Chapter review materials
include questions and application problems. Addi-
tional problems are available in the Study Guide
for GD&T: Application and Interpretation and in
the ExamView® Assessment Suite, which contains
more than 1700 questions.
Generally, tolerancing terms are defi ned
within the text when they are fi rst introduced.
Their defi nitions are repeated in the Glossary
to permit easy future reference. Other technical
terms are italicized when they fi rst appear. They
may be defi ned within the text or in the glossary.
Dimensioning and tolerancing terms used
within this textbook generally conform to those
used in the ASME standards. The terminology is
very specifi c to make possible an accurate explana-
tion of tolerance application and interpretation. After
a detailed term is defi ned, there are instances where
further application of the term is simplifi ed. An
explanation may refer to the centerline or “axis” of a
mating hole, rather than use a complex reference to
the “axis of the unrelated actual mating envelope”.
Illustrations are used extensively to clarify
explanations. Each fi gure generally introduces
only one new concept. Figures are not complicated
with detail that is unrelated to the concept being
explained. This makes it possible for the reader to
quickly see the necessary information.