The document outlines various Geometric Dimensioning and Tolerancing (GD&T) symbols and their applications, emphasizing their importance in ensuring the precision and functionality of mechanical components. Key symbols discussed include straightness, flatness, circularity, cylindricity, angularity, perpendicularity, parallelism, position, concentricity, symmetry, circular runout, and total runout. Each symbol is critical for maintaining specific design characteristics necessary for proper assembly and operation of parts like shafts, bearings, and rotating components.

1. GD&T symbols
and
applications
Muzmmil Shaikh

2. Straightness is used to
ensure that a feature,
such as a line or an axis,
maintains a straight form
along its length. It is
crucial in parts where
straight edges or features
are necessary for proper
function or assembly,
such as shafts or guide
rails.
1. Straightness

3. Controls the evenness of
a surface, ensuring that all
points on the surface lie
within two parallel
planes. This is particularly
important for mating
surfaces that must be
perfectly flat to ensure
proper sealing or contact,
like gasket surfaces or
precision-ground plates.
2. Flatness

4. Circularity controls the
roundness of a feature,
such as a cylinder or a
sphere, ensuring that all
points on the surface are
equidistant from the
centre. This is vital for
rotating parts, such as
bearings or Shafts, where
any deviation can lead to
imbalances
3. Circularity

5. This symbol ensures that
a cylindrical feature is
perfectly cylindrical
along its entire length,
maintaining consistent
diameter and form. It is
used in parts like
hydraulic cylinders or
piston rods, where
precision is crucial for
proper operation.
4. Cylindricity

6. The profile of a line
symbol controls the
contour of a line along a
surface, ensuring it
adheres to the specified
design within a tolerance
zone. This is useful where
the shape of a line can
significantly impact
performance.
5. Profile of a Line

7. This symbol controls the
contour of an entire
surface, ensuring that it
adheres to the design
specifications within a
tolerance zone. It is
essential for complex
surfaces, such as those
found in turbine blades or
automotive body panels.
6. Profile of a
Surface

8. Angularity ensures that a
feature is at a specified
angle relative to a datum.
This is important in parts
where precise angles are
necessary for assembly or
function, such as brackets
or mounting surfaces.
7. Angularity

9. The perpendicularity
symbol ensures that a
feature is at a right angle
(90 degrees) to a datum.
This is crucial for parts
that must assemble at
right angles, such as
frames or Angle plates,
ensuring stability and
proper alignment.
8. Perpendicularity

10. This symbol ensures that
a feature is parallel to a
datum within a specified
tolerance zone. It is used
in parts where parallelism
is critical for proper
function, such as sliding
components or parallel
shafts.
9. Parallelism

11. The position symbol
specifies the exact
location of a feature, such
as a hole or slot, relative
to a datum. This is one of
the most critical symbols
in GD&T, ensuring that
parts fit together
correctly in assemblies,
such as in dowel pin or
locating pins.
10. Position

12. Concentricity ensures
that the center of a
feature is in line with the
center of a datum axis. It
is used in parts where
multiple features must
share a common center,
such as in multi-axis
rotating components.
11. Concentricity

13. The symmetry symbol
ensures that features are
symmetrical about a
datum plane. This is
important in parts where
balanced and
symmetrical designs are
necessary for proper
function, such as in
balanced rotating parts
or mirrored components.
12. Symmetry

14. Circular runout controls
both the circularity and
coaxiality of a feature
when it is rotated around
a datum axis. This is used
in rotating components,
such as spindles or
wheels, to ensure smooth
operation and minimize
vibration.
13. Circular Runout

15. Total runout controls the
entire surface of a feature
relative to a datum axis,
ensuring that the feature
maintains its form and
orientation. This is crucial
for precision rotating
components, like shafts or
rotors, where any
deviation can lead to
performance issues.
14. Total Runout

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