GD&T Symbols and Rules — Questions and Answers

Question 1: Which GD&T symbol is used to control the orientation of a surface relative to a datum plane without controlling its location?

Parallelism (Correct answer)
Position
Flatness
Profile of a Surface

Correct answer: Parallelism

Parallelism controls the orientation of a surface or axis to be parallel to a datum without specifying its exact location.

Question 2: What does the 'S' modifier inside a feature control frame signify?

Statistical tolerancing
Spherical diameter (Correct answer)
Surface condition
Symmetrical tolerance

Correct answer: Spherical diameter

The 'S' prefix before a diameter symbol (Sø) indicates a spherical diameter in GD&T.

Question 3: Rule #2 in ASME Y14.5 states that unless otherwise specified, each tolerance of orientation, form, location, or runout applies to which condition?

Regardless of Feature Size (RFS) (Correct answer)
Maximum Material Condition (MMC)
Least Material Condition (LMC)
Free State (FST)

Correct answer: Regardless of Feature Size (RFS)

Rule #2 (RFS) is the default condition — geometric tolerances apply regardless of actual feature size unless MMC or LMC is specified.

Question 4: Which symbol in a feature control frame indicates that a tolerance applies to the full surface profile, including both sides of the tolerance zone equally?

Equal bilateral profile (no modifier) (Correct answer)
Unequal bilateral profile with 'U' symbol
All Around symbol
All Over symbol

Correct answer: Equal bilateral profile (no modifier)

A profile tolerance with no modifier defaults to equal bilateral disposition, split equally inside and outside the true profile.

Question 5: The 'all around' symbol on a leader line in a profile tolerance callout is represented by:

A circle at the bend of the leader line (Correct answer)
An arrow at both ends of the leader
The letters 'AR' in the feature control frame
A double-headed arrow on the leader

Correct answer: A circle at the bend of the leader line

A circle placed at the junction of the leader line and the reference line indicates that the profile tolerance applies all around the cross-section.

Question 6: In GD&T, what is the purpose of the datum feature symbol (a rectangle with a triangle)?

To identify a feature that serves as an origin for measurements (Correct answer)
To indicate a tolerance zone shape
To specify a material condition modifier
To denote a reference dimension

Correct answer: To identify a feature that serves as an origin for measurements

The datum feature symbol identifies physical features on a part that establish the coordinate system used for measurements and inspections.

Question 7: Which of the following GD&T symbols controls both the form and the orientation of a surface with respect to a datum?

Angularity (Correct answer)
Flatness
Straightness
Circularity

Correct answer: Angularity

Angularity controls the orientation of a surface or axis at a specified angle to a datum, inherently also controlling form within the tolerance zone.

Question 8: What does the 'free state' symbol (circle with the letter F) indicate in a GD&T callout?

The tolerance applies after release from manufacturing fixturing (Correct answer)
The part must be inspected while clamped
The feature is a free-turning axis
The tolerance applies only at room temperature

Correct answer: The tolerance applies after release from manufacturing fixturing

The free state modifier indicates that the geometric tolerance applies to the part in its unconstrained, free state — not held in a fixture.

Question 9: A profile of a line tolerance differs from a profile of a surface tolerance in that it:

Controls only a cross-sectional slice at any given location (Correct answer)
Controls the entire 3D surface simultaneously
Requires two datum references
Only applies to cylindrical features

Correct answer: Controls only a cross-sectional slice at any given location

Profile of a line controls the shape of a cross-sectional profile at individual cross-sections, while profile of a surface controls the complete 3D form.

Question 10: In a feature control frame, the compartment immediately following the tolerance value compartment contains:

The primary datum reference (Correct answer)
The geometric characteristic symbol
The material condition modifier for the tolerance
The bonus tolerance value

Correct answer: The primary datum reference

After the tolerance value (and any modifier on it), the next compartments list datum references in order: primary, secondary, then tertiary.

Question 11: Which symbol, when placed below a feature control frame, indicates that the tolerance applies to the entire length or surface — not per unit?

No additional symbol is needed; it applies to the entire extent by default (Correct answer)
An 'E' modifier in the frame
An underline beneath the frame
The 'T' symbol for total

Correct answer: No additional symbol is needed; it applies to the entire extent by default

By default, a geometric tolerance applies to the full extent of the feature unless a 'per unit' basis is specified separately below the frame.

Question 12: Which of the following is NOT a valid runout tolerance symbol in ASME Y14.5?

Total Runout of a Plane Surface (Correct answer)
Circular Runout
Total Runout
Runout of a Conical Surface

Correct answer: Total Runout of a Plane Surface

There is no separate GD&T symbol called 'Total Runout of a Plane Surface'; Total Runout (the arrow symbol) covers cylindrical and planar surfaces within one symbol.

Question 13: The diameter symbol (ø) placed before a tolerance value in a feature control frame means the tolerance zone is:

Cylindrical (Correct answer)
Equal in all directions on a flat plane
A width between two parallel lines
Spherical

Correct answer: Cylindrical

When ø precedes the tolerance value, the tolerance zone is a cylinder of that diameter surrounding the true axis or center.

Question 14: According to ASME Y14.5, which rule governs the relationship between size tolerance and form tolerance for an individual feature of size?

Rule #1 (Envelope Principle) (Correct answer)
Rule #2 (RFS Default)
Rule #3 (Datum Precedence)
Rule #4 (Virtual Condition)

Correct answer: Rule #1 (Envelope Principle)

Rule #1 (the Envelope Principle) states that the form of an individual feature of size must be within a perfect geometric envelope at MMC.

Question 15: A 'basic dimension' in GD&T is identified on a drawing by:

Enclosing the value in a rectangular box (Correct answer)
Adding the letters 'BSC' next to the value
Underlining the dimension value
Placing it in parentheses

Correct answer: Enclosing the value in a rectangular box

Basic dimensions are shown enclosed in a rectangular box and represent the exact theoretically perfect value from which toleranced dimensions are measured.

Question 16: What is the function of the 'tangent plane' modifier (T in a circle) in a GD&T callout?

The tolerance applies to a plane contacting the high points of the surface (Correct answer)
The tolerance applies only to tangent line elements
The feature must be tangent to the datum
The surface must be measured with a tangential probe

Correct answer: The tolerance applies to a plane contacting the high points of the surface

The tangent plane modifier means the tolerance controls the orientation of a tangent plane that contacts the high points of the surface, not the entire surface form.

Question 17: Which GD&T characteristic uses two coaxial cylinders as its tolerance zone?

Cylindricity (Correct answer)
Concentricity
Total Runout (on a cylindrical surface)
Circular Runout

Correct answer: Cylindricity

Cylindricity requires all points of a cylindrical surface to lie within two coaxial cylinders separated by the specified tolerance.

Question 18: The 'projected tolerance zone' symbol (P in a circle) is most commonly applied to:

Threaded holes or press-fit pins to control mating part interference (Correct answer)
Flat surfaces requiring parallelism
Profile tolerances on curved surfaces
Runout measurements on rotating shafts

Correct answer: Threaded holes or press-fit pins to control mating part interference

Projected tolerance zones extend the position tolerance above a hole to the height of the mating pin or fastener, preventing interference during assembly.

Question 19: In GD&T, the term 'virtual condition' for an external feature at MMC is calculated as:

MMC size plus the applicable geometric tolerance (Correct answer)
LMC size minus the applicable geometric tolerance
MMC size minus the applicable geometric tolerance
LMC size plus the applicable geometric tolerance

Correct answer: MMC size plus the applicable geometric tolerance

For an external feature (shaft) at MMC, virtual condition equals the MMC size plus the geometric tolerance, representing the worst-case boundary.

Question 20: Which symbol instructs the inspector to measure a feature while it is rotating about a datum axis?

Circular Runout or Total Runout (Correct answer)
Concentricity
Coaxiality
Cylindricity

Correct answer: Circular Runout or Total Runout

Both circular runout and total runout require the part to be rotated 360° about the datum axis while a fixed indicator records deviations.

Question 21: On a feature control frame, a datum letter followed by a material condition modifier (e.g., 'B(M)') means:

The datum shift allowance applies based on the actual mating size of datum feature B (Correct answer)
Datum B is measured at its maximum material boundary
The datum B reference is optional
Datum B must be re-established for each measurement

Correct answer: The datum shift allowance applies based on the actual mating size of datum feature B

Applying MMC to a datum reference allows datum shift — additional tolerance based on how far the datum feature departs from its MMC size.

GD&T Symbols and Rules

Which GD&T symbol is used to control the orientation of a surface relative to a datum plane without controlling its location?

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