5-156 Chapter Five
the profile tolerance of .010 establishes a discrete profile tolerance zone for each individual feature. As
with the Level 2 size limit boundaries for holes in a pattern, there is no basic relationship between these
Level 2 profile zones. They are all free to float relative to each other and relative to any datums. (Note: If
the Level 2 feature control frame were added as a third segment of the composite control, the Level 2
profile zones would be basically related to each other.) Of course, the Level 2 tolerance must be less than
any pattern-controlling tolerances to have any effect.
5.13.13 Composite Profile Tolerance for a Single Feature
For features of size, different characteristic symbols denote the four different levels of control. But, for
irregularly shaped nonsize features, the same “profile of a surface” symbol is used for each level. In Fig.
5-144, for example, we want to refine a bounded feature’s orientation within the constraints of its locating
tolerance. Simply stacking two single-segment profile feature control frames would be confusing. Many
people would question whether the .020 tolerance controls location relative to datum B. Instead, we’ve
borrowed from pattern control the composite feature control frame containing a single entry of the “profile
of a surface” symbol. Though our “pattern” has only one feature, the tolerances mean the same.
Figure 5-144 Composite profile tolerance for a single feature
In Fig. 5-144, the upper segment establishes a .080 wide profile tolerance zone basically located and
oriented relative to the DRF A|B|C. The lower segment provides a specialized refinement within the con-
straints of the upper segment. It establishes a .020 wide zone basically oriented, but not located, relative
to the DRF A|B. All the rules given in section 5.11.7.3 governing datum references, tolerance values, and
simultaneous requirements apply for a composite profile “pattern of one.”
5.14 Symmetry Tolerance
Symmetry is the correspondence in size, contour, and arrangement of part surface elements on opposite
sides of a plane, line, or point. We usually think of symmetry as the twofold mirror-image sort of balance
Geometric Dimensioning and Tolerancing 5-157
about a center plane shown in Fig. 5-145(a) and (b). There are other types as well. A three-lobe cam can
have symmetry, both the obvious twofold kind about a plane as shown in Fig. 5-145(c), and a threefold
kind about an axis as shown in Fig. 5-145(d). The pentagon shown in Fig. 5-145(e) has fivefold symmetry
about an axis. GD&T’s symmetry tolerances apply at the lowest order of symmetry—the lowest prime
divisor of the number of sides, facets, blades, lobes, etc., that the feature is supposed to have. Thus, a 27-

control. Otherwise, it would be impossible for any feature to conform.
5.14.2 How to Apply It
A symmetry tolerance is specified using a feature control frame displaying the characteristic symbol for
either “concentricity” (two concentric circles) or “symmetry about a plane” (three stacked horizontal
bars). See Figs. 5-146 through 5-148. The feature control frame includes the symmetry tolerance value
followed by one, two, or three datum references.
There’s no practical interaction between a feature’s size and the acceptable magnitude of lopsided-
ness. Thus, material condition modifier symbols, MMC and LMC, are prohibited for all symmetry toler-
ances and their datum references.
5.14.3 Datums for Symmetry Control
Symmetry control requires a DRF. A primary datum plane or axis usually arrests the three or four degrees
of freedom needed for symmetry control. All datum references shall be RFS.
Figure 5-147 Symmetry tolerance about a datum plane
5-160 Chapter Five
5.14.4 Concentricity Tolerance
Concentricity tolerancing of a revolute, as illustrated in Fig. 5-146, is one of the most common applications
of symmetry tolerancing. It’s specified by a feature control frame containing the “concentricity” symbol.
In this special symmetry case, the datum is an axis. There are two rays 180° apart (colinear) perpendicular
to the datum axis. The rays intersect the feature surface at two diametrically opposed points. The midpoint
between those two surface points shall lie within a cylindrical tolerance zone coaxial to the datum and
having a diameter equal to the concentricity tolerance value.
At each cross-sectional slice, the revolving rays generate a locus of distinct midpoints. As the rays
sweep the length of the controlled feature, these 2-D loci of midpoints stack together, forming a 3-D
“wormlike” locus of midpoints. The entire locus shall be contained within the concentricity tolerance
cylinder. Don’t confuse this 3-D locus with the 1D derived median line defined in section 5.6.4.2.
5.14.4.1 Concentricity Tolerance for Multifold Symmetry about a Datum Axis
The explanation of concentricity in Y14.5 is somewhat abstruse because it’s also meant to support multifold
symmetry about an axis. Any prime number of rays can be projected perpendicular from the datum axis,
provided they are coplanar with equal angular spacing. For the 3-lobe cam in Fig. 5-148, there are three
rays, 120° apart. A 25-blade impeller would require five rays spaced 72° apart, etc.

ness of surface line elements. Again, the objective is that the part’s mass be equally distributed about the
datum. Although a symmetry or concentricity tolerance provides little or no form control, it always accom-
panies a size dimension that provides some restriction on form deviation according to Rule #1.
5.14.6 Symmetry Tolerancing of Yore (Past Practice)
Until the 1994 edition, Y14.5 described concentricity tolerancing as an “axis” control, restraining a sepa-
rate “axis” at each cross-section of the controlled feature. A definition was not provided for axis, nor was
there any explanation of how a two-dimensional imperfect shape (a circular cross-section) could even
have such a thing. As soon as the Y14.5 Subcommittee defined the term feature axis, it realized two things
about the feature axis: it’s what ordinary positional tolerance RFS controls, and it has nothing to do with
lopsidedness (balance). From there, symmetry rays, median points, and worms evolved.
The “Symmetry Tolerance” of the 1973 edition was exactly the same as positional tolerance applied to
a noncylindrical feature RFS. (See the note at the bottom of Fig. 140 in that edition.) The three-horizontal
bars symbol was simply shorthand, saving draftsmen from having to draw circle-S symbols. Partly be-
cause of its redundancy, the “symmetry tolerance” symbol was cut from the 1982 edition.
5-162 Chapter Five
5.14.7 When Do We Use a Symmetry Tolerance?
Under any symmetry tolerance, a surface element on one “side” of the datum can “do anything it wants”
just as long as the opposing element(s) mirrors it. This would appear to be useful for a rotating part that
must be dynamically balanced. However, there are few such assemblies where GD&T alone can ad-
equately control balance. More often, the assembly includes setscrews, keyseats, welds, or other attach-
ments that entail a balancing operation after assembly. And ironically, a centerless ground shaft might
have near-perfect dynamic balance, yet fail the concentricity tolerance because its out-of-roundness is
3-lobed.
FAQ: Could a note be added to modify the concentricity tolerance for a cylinder to 3-fold symmetry?
A: Sure.
FAQ: Can I use a symmetry tolerance if the feature to be controlled is offset (not coaxial or
coplanar) from the datum feature?
A: Nothing in the standard prohibits that, either. Be sure to add a basic dimension to specify the
offset. You may also need two or even three datum references.
FAQ: Since a runout tolerance includes concentricity control and is easier to check, wouldn’t it

must understand the controls imposed at each level by a given tolerance. For example, where a Level 4
(location) tolerance has been maximized, it might not adequately restrict orientation. Thus, a separate
lesser Level 3 (orientation) tolerance must be added. Even that tolerance, if properly maximized, might not
adequately control 3-D form, etc. That’s why it’s not uncommon to see two, or even three feature control
frames stacked for one feature, each maximizing the tolerance at a different level.
5.16 “Instant” GD&T
Y14.5 supports several general quasi-GD&T practices as alternatives to the more rigorous methods we’ve
covered. To be fair, they’re older practices that evolved as enhancements to classical tolerancing meth-
ods. However, despite the refinement and proliferation of more formal methods, the quasi-GD&T practices
are slow to die and you’ll still see them used on drawings. Designers might be tempted to use one or two
of them to save time, energy, and plotter ink. We’ll explain why, for each such practice, we feel that’s false
economy.
5.16.1 The “Dimension Origin” Symbol
The “dimension origin” symbol, shown in Fig. 5-149, is not associated with any datum feature or any
feature control frame. It’s meant to indicate that a dimension between two features shall originate from
one of these features and not the other. The specified treatment for the originating surface is exactly the
same as if it were a primary datum feature. But for some unfathomable reason, Y14.5 adds, This concept
does not establish a datum reference frame… The treatment for the other surface is exactly the same as
if it were controlled with a profile of a surface tolerance. We explained in section 5.10.8 why this practice
is meaningless for many angle dimensions. Prevent confusion; instead of the “dimension origin” symbol,
use a proper profile or positional tolerance.
Figure 5-149 Dimension origin symbol
5.16.2 General Note to Establish Basic Dimensions
Instead of drawing the “basic dimension” frame around each basic dimension, a designer may designate
dimensions as basic by specifying on the drawing (or in a document referenced on the drawing) the
general note: UNTOLERANCED DIMENSIONS LOCATING TRUE POSITION ARE BASIC. This
could be extremely confusing where other untoleranced dimensions are not basic, but instead default to
tolerances expressed in a tolerance block. Basic dimensions for angularity and profile tolerances, datum
targets, and more would still have to be framed unless the note were modified. Either way, the savings in
ink are negligible compared to the confusion created. Just draw the frames.

a process capability requirement.
History teaches us that new technology comes faster than we ever expected. Regardless of our
apprehension about that, history also reveals that old technology lingers on longer than we expected. In
fact, the better the technology, the slower it dies. An excellent example is the audio Compact Cassette,
introduced to the world by Philips in 1963. Even though Compact Discs have been available in every
music store since 1983, about one-fourth of all recorded music is still sold on cassette tapes. We can
likewise expect material removal processes and some form of GD&T to enjoy widespread use for at least
another two decades, regardless of new technology.
In its current form, GD&T reflects its heritage as much as its aspirations. It evolved in relatively small
increments from widespread, time-tested, and work-hardened practices. As great as it is, GD&T still has
much room for improvement. There have been countless proposals to revamp it, ranging from moderate
streamlining to total replacement. Don’t suppose for one second that all such schemes have been hare-
brained. One plan, for example, would define part geometry just as a coordinate measuring machine sees
it—vectorially. Such a system could expedite automated inspection, and be simpler to learn. But does it
preclude measurements with simple tools and disenfranchise manufacturers not having access to a CMM?
What about training? Will everyone have to be fluent in two totally different dimensioning and toleranc-
ing languages?
Geometric Dimensioning and Tolerancing 5-165
As of this writing, the international community is much more receptive to radical change than the US.
Europe is a hotbed of revolutionary thought; any daring new schemes will likely surface there first.
Americans can no longer play isolationism as they could decades ago. Many US companies are engaged
in multinational deals where a common international drawing standard is mandatory. Those companies are
scarcely able to insist that standard be Y14.5. There are always comments about “the tail wagging the
dog,” but the US delegation remains very influential in ISO TC 213 activity pertaining to GD&T. Thus, in
the international standards community, it’s never quite clear where the tail ends and the dog begins.
Meanwhile, Americans are always looking for ways to simplify GD&T, to make their own Y14.5
Standard thinner (or at least to slow its weight gain). You needn’t study GD&T long to realize that a few
characteristic symbols are capable of controlling many more attributes than some others control. For
example, a surface profile tolerance can replace an equal flatness tolerance. Why do we need the “flat-
ness” symbol? And if the only difference between parallelism, perpendicularity, and angularity is the basic

345 East 47th Street
New York, NY 10017
5-166 Chapter Five
5.18 References
1. The American Society of Mechanical Engineers. 1972. ANSI B89.3.1-1972. Measurement of Out-Of-Roundness.
New York, New York: The American Society of Mechanical Engineers.
2. The American Society of Mechanical Engineers. 1972. ANSI B4.1-1967. Preferred Limits and Fits for
Cylindrical Parts. New York, New York: The American Society of Mechanical Engineers.
3. The American Society of Mechanical Engineers. 1978. ANSI B4.2-1978. Preferred Metric Limits and Fits. New
York, New York: The American Society of Mechanical Engineers.
4. The American Society of Mechanical Engineers. 1982. ANSI Y14.5M-1982, Dimensioning and Tolerancing.
New York, New York: The American Society of Mechanical Engineers.
5. The American Society of Mechanical Engineers. 1995. ASME Y14.5M-1994, Dimensioning and Tolerancing.
New York, New York: The American Society of Mechanical Engineers.
6. The American Society of Mechanical Engineers. 1994. ASME Y14.5.1-Mathematical Definition of Dimensioning
and Tolerancing Principles. New York, New York: The American Society of Mechanical Engineers.
7. International Standards Organization. 1985. ISO8015. Technical Drawings Fundamental Tolerancing Principle.
International Standards Organization: Switzerland.
6-1
Differences Between US Standards
and Other Standards
Alex Krulikowski
Scott DeRaad
Alex Krulikowski
General Motors Corporation
Westland, Michigan
A Standards manager at General Motors and a member of SME and AQC, Mr. Krulikowski has written
articles for several magazines and speaks frequently at public seminars and in-house training pro-
grams. He has written 12 books on dimensioning and tolerancing, produced videotapes, computer
based training, and other instructional materials. He serves on several corporate and national commit-

The ASME Y14.5M-1994 Dimensioning and Tolerancing Standard covers all the topics of dimension-
ing and tolerancing. The Y14.5 standard is 232 pages long and is updated about once every ten years. The
other Y14 standards in Table 6-1 are ASME standards that provide terminology and examples for the
interpretation of dimensioning and tolerancing of specific applications.
Subcommittees of ASME create ASME standards. Each subcommittee consists of representatives
from industry, government organizations, academia, and consultants. There are typically 8 to 25 members
on a subcommittee. Once the subcommittee creates a draft of a standard, it goes through an approval
process that includes a public review. (Reference 5)
6.1.2 International Standards
Outside the United States, the most common standards for dimensioning are established by the Interna-
tional Organization for Standardization (ISO). ISO is a worldwide federation of 40 to 50 national standards
bodies (ISO member countries). The ISO federation publishes hundreds of standards on various topics. A
list of the ISO standards that are related to dimensioning is shown in Table 6-2.
STD
Number Title STD Date
Y14.5M Dimensioning and Tolerancing 1994
Y14.5.1M Mathematical Definition of Dimensioning and 1994
Tolerancing Principles
Y14.8M Castings and Forgings 1996
Y14.32.1 Chassis Dimensioning Practices 1994
Differences Between US Standards and Other Standards 6-3
STD
Number Title STD Date
128 Technical Drawings - General principles of presentation 1982
129
Technical Drawings - Dimensioning - General principles,
definitions, methods of execution and special indications
1985
406 Technical Drawings - Tolerancing of linear and angular dimensions 1987
1101

1983
8015 Technical drawings - Fundamental tolerancing principle 1985
10209-1
Technical product documentation vocabulary - Part 1: Terms
relating to technical drawings - General and types of drawings
1992
10578
Technical drawings - Tolerancing of orientation and location -
Projected tolerance zone
1992
10579
Technical drawings - Dimensioning and tolerancing - Non-rigid
parts
1993
13715
Technical drawings - Corners of undefined shape - Vocabulary
and indication on drawings
1997
Table 6-2 ISO standards that are related to dimensioning
6-4 Chapter Six
The ISO standards divide dimensioning and tolerancing into topic subsets. A separate ISO standard
covers each dimensioning topic. The standards are typically short, approximately 10 to 20 pages in length.
When using the ISO standards for dimensioning and tolerancing, it takes 15 to 20 standards to cover all
the topics involved.
The work of preparing international standards is normally carried out through ISO technical commit-
tees. Each country interested in a subject for which a technical committee has been established has the
right to be represented on that committee. International organizations, governmental and nongovernmen-
tal, in liaison with ISO, also take part in the work. The ISO standards are an agreement of major points
among countries. Many companies (or countries) that use the ISO dimensioning standards also have
additional dimensioning standards to supplement the ISO standards.

Standards
Differences Between US Standards and Other Standards 6-5
6.2 Comparison of ASME and ISO Standards
Most worldwide dimensioning standards used in industry are based on either the ASME or ISO dimen-
sioning standards. These two standards have emerged as the primary dimensioning standards. In the
United States, the ASME standard is used in an estimated 90% of major corporations.
The ASME and ISO standards organizations are continually making revisions that bring the two
standards closer together. Currently the ASME and ISO dimensioning standards are 60 to 70% common.
It is predicted that in the next five years the two standards will be 80 to 90% common. Some industry
experts predict that the two dimensioning standards will be merged into a single common standard some-
time in the future. (Reference 5)
6.2.1 Organization and Logistics
An area of difference between ASME and ISO standards is in the organization and logistics of documen-
tation. With regards to the approach to dimensioning in the ASME and ISO standards, the ASME
standard uses product function as the primary basis for establishing tolerances. This is supported with
numerous illustrated examples of tolerancing applications throughout the ASME standard. The ISO di-
mensioning standard is more theoretical in its explanation of tolerancing. It contains a limited number of
generic examples that explain the interpretation of tolerances, with functional application a lesser consid-
eration. Table 6-4 summarizes the differences between standards. (Reference 5)
Table 6-4 Differences between ASME and ISO standards
Item ASME Y14.5M-1994 ISO
Approach to Functional Theoretical
dimensioning
Level of explanation Thorough explanation and Minimal explanations, select
complementary illustrations examples
Number of standards Single standard Multiple Standards (15-20 separate
publications)
Revision frequency About every ten years Select individual standards change
yearly
Cost of standards Less than $100 USD $700 - $1000 USD

and tolerancing is contained in one create and revise than does a shorter
document. document.
ASME Y14.5M-1994 Relatively infrequent revisions allow If an error is in the document, it will
Single Standard industry to thoroughly integrate the be around for a long time.
standard into the workforce.
Ensures that the terms and concepts
are at the same revision level at the
time of publication.
Easy to specify and understand which
standards apply to a drawing for
dimensioning and tolerancing.
Shorter documents can be created and Industry needs adequate time to
revised in less time than a longer integrate new standards into the
document. workforce. Training, software
development, and multiple standards
all require time to address.
ISO Additional topics can be added New or revised standards may
Multiple Standards without revising all the existing introduce terms or concepts that
standards. conflict with other existing standards.
Multiple standards have multiple
revision dates.
Can be difficult to determine which
standards apply to a drawing.
One belief is the ISO standards that
are in effect on the date of the drawing
are the versions that apply to the
drawing. This method is indirect, and
many drawing users do not know
which standards are in effect for a
given date.

the countersink. (3.3.13)
None
Dimensioned by showing either the required
diametral dimension at the surface and the included
angle, or the depth and the included angle. (#129,
6.4.2)
General
Reprinted by permission of Effective Training Inc.
Table 6-6A General
6-8 Chapter Six
Diameter symbol usage
Diameter symbol may be omitted where the
shape is clearly defined. (#129, 4.4.4)
SYMBOL OR EXAMPLE SYMBOL OR EXAMPLE
Depth / Deep Use a note
ASME Y14.5M-1994 ISO
Concept / Term
None
Diameter symbol precedes all diametral values.
(1.8.1)
Symbolic means of indicating that a dimension
applies to the depth of a feature. (3.3.14)
Feature control frame
Tolerance frame (#1101, 5.1)Feature control frame (3.4)
Extension (Projection)
lines
Extension lines start from the outline of the part
without any gap. (#129,4.2)
Extension lines start with a short visible gap
from the outline of the part (1.7.2)

(#1101, 7)
General
Reprinted by permission of Effective Training Inc.
Table 6-6B General
Differences Between US Standards and Other Standards 6-9
Table 6-6C General
Concept / Term
SYMBOL OR EXAMPLE SYMBOL OR EXAMPLE
ISOASME Y14.5M-1994
General tolerances
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Regardless of feature
size (RFS)
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RFS applies, with respect to the individual
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RFS by default (no exceptions) (#8015,5.2)
None
Default
Rule #2a, For a tolerance of position, RFS may
be specified on the drawing with respect to the
individual tolerance, datum reference, or both,
as applicable. (2.8)
Screw threads
None
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orientation or position and datum reference
specified for a screw thread applies to the axis
of the thread derived from the pitch cylinder.
(2.9, 2.10, 4.5.9)
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General
Reprinted by permission of Effective Training Inc.
Table 6-6D General
Differences Between US Standards and Other Standards 6-11
Table 6-6E General

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the feature control frame after the stated
tolerance. (6.6.1.3)
Tangent plane modifier
T
None None
Third angle projection (1.2)
80°
First angle projection (#128)
0.1
Part
A
A
Tolerance zone
A
0,1
80°
A
General
Reprinted by permission of Effective Training Inc.
0,1
0.1
Differences Between US Standards and Other Standards 6-13
Flatness
Flatness can only be applied to a single
surface. (6.4.2)
(Profile is used to control flatness / coplanarity
of multiple surfaces (6.5.6.1))
Flatness can be applied to a single surface or
flatness can have a single tolerance frame