This document provides an overview of geometric dimensioning and tolerancing (GD&T). It defines three categories of dimensioning: general, geometric, and surface texture. GD&T is important as it saves money by reducing unnecessary inspection of features, ensures interchangeability, and provides a universal understanding of symbols. GD&T should be used when part features are critical to function or interchangeability. The document provides examples of when and how to apply GD&T to features such as flatness, straightness, and circularity.

1. Geometric Dimensioning and
Tolerances (GD&T)

2. PART PRODUCTION COMMUNICATION MODEL
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ROUTING
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CUSTOMERSVENDORS
Geometric Dimensioning and
Tolerancing (GD&T)

3. Dimensioning can be divided into three
categories:
•general dimensioning,
•geometric dimensioning, and
•surface texture.
The following provides information necessary
to begin to understand geometric
dimensioning and tolerancing (GD&T)
Three Categories of
Dimensioning

4. WHY IS GD&T IMPORTANT
• Saves money
– For example, if large number of parts are being
made – GD&T can reduce or eliminate
inspection of some features.
– Provides “bonus” tolerance
• Ensures design, dimension, and tolerance
requirements as they relate to the actual function
• Ensures interchangeability of mating parts at the
assembly
• Provides uniformity
• It is a universal understanding of the symbols
instead of words

5. WHEN TO USE GD&T
• When part features are critical to a function or
interchangeability
• When functional gaging is desirable
• When datum references are desirable to ensure
consistency between design
• When standard interpretation or tolerance is not
already implied
• When it allows a better choice of machining
processes to be made for production of a part

6. Geometric Tolerancing Applied To
An Angle Block

7. Geometric Dimensioning &
Tolerancing (GD&T)
• GD&T is a means of dimensioning &
tolerancing a drawing which considers the
function of the part and how this part
functions with related parts.
– This allows a drawing to contain a more
defined feature more accurately, without
increasing tolerances.

8. For Example
• Given Table Height
• However, all surfaces have a degree of waviness, or
smoothness. For example, the surface of a 2 x 4 is much wavier
(rough) than the surface of a piece of glass.
– As the table height is dimensioned, the following table would pass
inspection.
• If top must be flatter, you could tighten the tolerance to ±
1/32.
– However, now the height is restricted to 26.97 to 27.03 meaning good
tables would be rejected.
Assume all 4 legs will be cut to
length at the same time.
or

9. Example cont’d.
• You can have both, by using GD&T.
– The table height may any height between 26 and
28 inches.
– The table top must be flat within 1/16. (±1/32)
27
.06
26
.06
28
.06

10. TERMINOLOGY REVIEW
• Maximum Material Condition (MMC): The condition
where a size feature contains the maximum amount of
material within the stated limits of size. I.e., largest shaft
and smallest hole.
• Least Material Condition (LMC): The condition where a
size feature contains the least amount of material within
the stated limits of size. I.e., smallest shaft and largest
hole.
• Tolerance: Difference between MMC and LMC limits of a
single dimension.
• Allowance: Difference between the MMC of two mating
parts. (Minimum clearance and maximum interference)
• Basic Dimension: Nominal dimension from which
tolerances are derived.

11. THIS MEAN?
WHAT DOES
SIZE DIMENSION
2.007
2.003
LIMITS OF SIZE

12. SIZE DIMENSION
MMC
LMC
ENVELOPE OF SIZE
(2.003)
(2.007)
ENVELOPE PRINCIPLE
LIMITS OF SIZE
A variation in form is allowed between the least material condition (LMC)
and the maximum material condition (MMC).
Envelop Principle defines the size and
form relationships between mating parts.

13. ENVELOPE PRINCIPLE
LMC
CLEARANCE
MMC
ALLOWANCE
LIMITS OF SIZE

14. LIMITS OF SIZE
The actual size of the feature at any cross section must be within the size
boundary.
ØMMC
ØLMC

15. No portion of the feature may be outside a perfect form barrier at
maximum material condition (MMC).
LIMITS OF SIZE

16. INDIVIDUAL (No
Datum
Reference)
INDIVIDUAL or
RELATED
FEATURES
RELATED
FEATURES
(Datum
Reference
Required)
GEOMETRIC CHARACTERISTIC CONTROLS
TYPE OF
FEATURE
TYPE OF
TOLERANCE CHARACTERISTIC SYMBOL
SYMMETRY
FLATNESS
STRAIGHTNESS
CIRCULARITY
CYLINDRICITY
LINE PROFILE
SURFACE PROFILE
PERPENDICULARITY
ANGULARITY
PARALLELISM
CIRCULAR RUNOUT
TOTAL RUNOUT
CONCENTRICITY
POSITION
FORM
PROFILE
ORIENTATION
RUNOUT
LOCATION
14 characteristics that may be controlled

17. Characteristics & Symbols cont’d.
– Maximum Material Condition MMC
– Regardless of Feature Size RFS
– Least Material Condition LMC
– Projected Tolerance Zone
– Diametrical (Cylindrical) Tolerance Zone or Feature
– Basic, or Exact, Dimension
– Datum Feature Symbol
– Feature Control Frame

18. THE
GEOMETRIC SYMBOL
TOLERANCE INFORMATION
DATUM REFERENCES
FEATURE CONTROL FRAME
COMPARTMENT VARIABLES
CONNECTING WORDS
MUST BE WITHIN
OF THE FEATURE
RELATIVE TO
Feature Control Frame

19. Feature Control Frame
• Uses feature control frames to indicate tolerance
• Reads as: The position of the feature must be within
a .003 diametrical tolerance zone at maximum
material condition relative to datums A, B, and C.

20. Feature Control Frame
• Uses feature control frames to indicate tolerance
• Reads as: The position of the feature must be within a
.003 diametrical tolerance zone at maximum material
condition relative to datums A at maximum material
condition and B.

21. Placement of Feature Control
Frames
May be attached to a side, end or corner of the
symbol box to an extension line.
Applied to surface.
Applied to axis

22. Placement of Feature Control
FramesCont’d.
May be below or closely adjacent to the
dimension or note pertaining to that feature.
Ø .500±.005

23. Basic Dimension cont’d.

24. Form FeaturesExamples
Flatness as stated on drawing: The flatness
of the feature must be within .06 tolerance
zone.
.003
0.500 ±.005
.003
0.500 ±.005
Straightness applied to a flat surface: The straightness of the
feature must be within .003 tolerance zone.

25. Form FeaturesExamples
Straightness applied to the surface of a diameter: The
straightness of the feature must be within .003 tolerance zone.
.003
0.500
0.505
Straightness of an Axis at MMC: The derived median line
straightness of the feature must be within a diametric zone of .030
at MMC.
.0300.500
0.505 M
1.010
0.990