GD&T Geometric Symbols & Notation — Questions and Answers

Question 1: What does the symbol ⌀ represent in GD&T?

Radius of a circle.
Diameter of a circle. (Correct answer)
The center of a circle.
The length of a side in a square.

Correct answer: Diameter of a circle.

In Geometric Dimensioning and Tolerancing (GD&T), the symbol ⌀ is universally recognized as the diameter symbol. It is used to indicate that a dimension refers to the diameter of a circular feature, such as a hole, shaft, or boss. This ensures clarity and precision in engineering drawings, distinguishing it from a radius or other linear dimensions.

Question 2: What does the symbol x signify in GD&T?

Multiplication factor for tolerances. (Correct answer)
A symbol for angular measurements.
Maximum allowable dimension.
A mark for reference dimensions.

Correct answer: Multiplication factor for tolerances.

In GD&T, the 'x' symbol, often appearing before a dimension (e.g., 2x ⌀10), indicates a multiplication factor. It specifies that a feature or pattern is repeated a certain number of times. For example, '2x ⌀10' means there are two holes, each with a diameter of 10 units, and the tolerance applies to both.

Question 3: Which symbol is used to indicate flatness in GD&T?

⌀.
F.
⎯⎯. (Correct answer)
⊗.

Correct answer: ⎯⎯.

The symbol ⎯⎯ (two parallel lines) is the standard GD&T symbol for flatness. This geometric characteristic tolerance specifies how much a surface is permitted to deviate from a perfect plane. It ensures that all points on the designated surface lie within two parallel planes, thereby controlling the overall evenness of the feature.

Question 4: What is the purpose of the perpendicularity symbol in GD&T?

Indicates symmetry of a feature.
Ensures a feature is square to a reference surface. (Correct answer)
Determines the size of the feature.
Checks the center of a circle.

Correct answer: Ensures a feature is square to a reference surface.

The perpendicularity symbol (⊥) in GD&T is a form tolerance that controls the orientation of a feature relative to a datum (a reference feature). It specifies that a surface, axis, or center plane must be at a 90-degree angle to a designated datum feature. This ensures that components align correctly during assembly and function as intended.

Question 5: What does the angularity symbol control in GD&T?

Angle between two surfaces.
Angle between a feature and the reference plane. (Correct answer)
Angle of rotation.
Angle of deviation.

Correct answer: Angle between a feature and the reference plane.

The angularity symbol (∠) in GD&T is an orientation tolerance that controls the angle of a feature relative to a datum plane or axis. It specifies the allowable deviation from a true angle, typically a non-90-degree angle, between the feature and the specified reference. This ensures that angled surfaces or features are correctly oriented for proper assembly and function.

Question 6: Which symbol indicates a location of a feature in GD&T?

⌀.
⊥.
☒.
◯. (Correct answer)

Correct answer: ◯.

The symbol ◯ (a circle) in GD&T represents 'position' or 'true position.' It is a location tolerance used to define the allowable variation in the location of a feature, such as a hole or slot, relative to a datum reference frame. This ensures that features are placed accurately on a part, which is critical for assembly and interchangeability.

Question 7: How is the concentricity symbol used in GD&T?

To ensure the feature is centered on the datum axis. (Correct answer)
To determine the radius of a hole.
To determine the symmetry of a feature.
To control angularity.

Correct answer: To ensure the feature is centered on the datum axis.

The concentricity symbol (two concentric circles) in GD&T is a form of runout tolerance used to control the relationship of two or more features that share a common axis. It ensures that the median points of a feature's cross-sections are contained within a cylindrical tolerance zone, which is coaxial with a datum axis. This is crucial for rotating parts to prevent wobble or imbalance.

Question 8: What is the purpose of a profile of a surface in GD&T?

To define the feature’s size.
To define the flatness of a surface.
To control the outline of a feature. (Correct answer)
To define the roundness of a feature.

Correct answer: To control the outline of a feature.

Profile of a surface is a GD&T tolerance that defines a 3D tolerance zone along the entire surface of a feature. It controls the shape, size, orientation, and location of complex or irregular surfaces, ensuring that the actual surface does not deviate beyond the specified boundaries. This is particularly useful for features that cannot be easily defined by other geometric tolerances.

Question 9: What does the profile of a line control in GD&T?

The center of a circle.
The contour of a feature. (Correct answer)
The angle of a feature.
The length of a side.

Correct answer: The contour of a feature.

Profile of a line in GD&T is a 2D tolerance that controls the contour of a feature along a specific cross-section. It defines a tolerance zone that extends along the length of the feature, ensuring that all points on that line segment lie within the specified boundaries. This is used for features where the cross-sectional shape is critical, but the entire surface profile might not be.

GD&T Geometric Symbols & Notation

What does the symbol ⌀ represent in GD&T?