GD&T Form and Orientation Tolerances — Questions and Answers

Question 1: Which GD&T symbol is used to control the straightness of a surface element (line element) on a cylindrical part?

Flatness (⏥)
Straightness (⏤) (Correct answer)
Circularity (○)
Cylindricity (⌀)

Correct answer: Straightness (⏤)

Straightness controls individual line elements on a surface or the derived median line of a feature of size.

Question 2: A flatness tolerance zone is defined as the space between two:

Concentric cylinders
Parallel planes (Correct answer)
Parallel lines
Coaxial spheres

Correct answer: Parallel planes

Flatness tolerance zone consists of two parallel planes within which the entire surface must lie.

Question 3: When angularity is applied to a surface, what is the shape of the tolerance zone?

Two parallel planes at the specified angle to the datum (Correct answer)
A cylinder at the specified angle
A cone at the specified angle
Two parallel lines at the specified angle

Correct answer: Two parallel planes at the specified angle to the datum

Angularity applied to a surface creates a tolerance zone of two parallel planes oriented at the specified angle relative to the datum.

Question 4: Cylindricity differs from circularity in that cylindricity controls:

Only cross-sectional roundness
Both the roundness and straightness of the entire surface simultaneously (Correct answer)
The axis orientation only
The diameter variation only

Correct answer: Both the roundness and straightness of the entire surface simultaneously

Cylindricity simultaneously controls circularity, straightness, and taper of the entire cylindrical surface in a single tolerance.

Question 5: Which statement about form tolerances and datums is correct?

Form tolerances always require at least one datum reference
Form tolerances never reference datums (Correct answer)
Flatness requires a datum but circularity does not
Straightness always requires a datum axis

Correct answer: Form tolerances never reference datums

Form tolerances (flatness, straightness, circularity, cylindricity) by definition control the shape of an individual feature and never require datum references.

Question 6: A perpendicularity callout on a pin's axis controls the orientation of the pin's derived median line relative to:

Its own surface
A referenced datum plane or axis (Correct answer)
The part's largest feature
Any convenient reference

Correct answer: A referenced datum plane or axis

Perpendicularity applied to an axis controls how closely the feature's derived median line is 90° to the referenced datum.

Question 7: Under ASME Y14.5, the circularity (roundness) tolerance value must be:

Greater than the size tolerance
Less than or equal to the size tolerance (Correct answer)
Equal to the cylindricity tolerance
Independent of the size tolerance

Correct answer: Less than or equal to the size tolerance

Per Rule #1 (Envelope Principle), the circularity tolerance cannot exceed the size tolerance because the feature must remain within its size limits.

Question 8: What does it mean when a straightness tolerance is applied to the derived median line of a shaft rather than its surface?

The surface elements must be straight
Rule #1 is overridden and the shaft axis may bow outside the MMC boundary (Correct answer)
The shaft must be perfectly round
The size tolerance is tightened

Correct answer: Rule #1 is overridden and the shaft axis may bow outside the MMC boundary

Straightness of the derived median line overrides Rule #1, allowing the axis to bend outside the perfect-form-at-MMC boundary while the shaft remains within size limits at each cross-section.

Question 9: A parallelism tolerance of 0.05 mm applied to a surface means the surface must lie between two planes that are parallel to the datum and separated by:

0.025 mm
0.05 mm (Correct answer)
0.10 mm
The size tolerance value

Correct answer: 0.05 mm

The tolerance value of 0.05 mm directly defines the width of the tolerance zone between the two parallel planes.

Question 10: Which orientation tolerance would you use to ensure a drilled hole is exactly 90° to a datum surface?

Angularity
Parallelism
Perpendicularity (Correct answer)
Tilt

Correct answer: Perpendicularity

Perpendicularity is the orientation tolerance specifically defined for 90° relationships between a feature and a datum.

Question 11: On a GD&T drawing, a circularity tolerance of 0.02 applied to a sphere means:

Every cross-section through the center must have a roundness within 0.02 (Correct answer)
The sphere's diameter cannot vary more than 0.02
The sphere's center must lie within a 0.02 zone
Every cross-section in one direction must be within 0.02

Correct answer: Every cross-section through the center must have a roundness within 0.02

Circularity on a sphere requires every cross-section passing through the center to be circular within the tolerance value.

Question 12: Which of the following best describes the cylindricity tolerance zone?

Two coaxial cylinders between which the surface must lie (Correct answer)
Two parallel planes between which the surface must lie
A single cylinder the surface must not exceed
A cone that the surface must fit within

Correct answer: Two coaxial cylinders between which the surface must lie

Cylindricity's tolerance zone consists of two coaxial (same-axis) cylinders; the entire surface must fall between them.

Question 13: An angularity tolerance applied to a hole axis at 45° to a datum controls the hole axis within a:

Cylindrical zone oriented at 45° to the datum (Correct answer)
Planar zone oriented at 45° to the datum
Conical zone at 45°
Spherical zone centered at 45°

Correct answer: Cylindrical zone oriented at 45° to the datum

When angularity is applied to an axis (feature of size), the tolerance zone is a cylinder oriented at the specified angle to the datum.

Question 14: What is the primary difference between flatness and parallelism?

Flatness uses a datum; parallelism does not
Parallelism requires a datum reference; flatness does not (Correct answer)
Both always require datums
Neither requires a datum

Correct answer: Parallelism requires a datum reference; flatness does not

Flatness controls a surface's form independently with no datum, while parallelism controls a surface's orientation relative to a referenced datum.

Question 15: A feature control frame shows perpendicularity with an MMC modifier (Ⓜ) applied to a pin. As the pin's actual size departs from MMC, the perpendicularity tolerance:

Decreases by the same amount
Remains fixed
Increases by the same amount as the departure (Correct answer)
Doubles

Correct answer: Increases by the same amount as the departure

The MMC modifier creates a bonus tolerance: for each unit the pin departs from MMC toward LMC, the perpendicularity tolerance increases by one unit.

Question 16: Which GD&T control is most appropriate to ensure two mating flat surfaces will make full contact (not rock)?

Parallelism
Flatness (Correct answer)
Straightness
Profile of a Surface

Correct answer: Flatness

Flatness controls how planar a single surface is, preventing rocking or wobble when two surfaces are mated.

Question 17: Under ASME Y14.5-2018, which modifier can be applied to straightness of a derived median line to allow additional tolerance?

Least Material Condition (LMC) only
Maximum Material Condition (MMC) or Least Material Condition (LMC) (Correct answer)
Free State (F) only
Projected Tolerance Zone (P) only

Correct answer: Maximum Material Condition (MMC) or Least Material Condition (LMC)

Straightness of a derived median line may use MMC or LMC modifiers to grant bonus tolerance as the feature departs from the specified material condition.

Question 18: A parallelism callout of 0.1 on a surface with datum A means the surface must:

Be within 0.1 of the nominal distance from datum A
Lie between two planes 0.1 apart and parallel to datum A (Correct answer)
Not deviate from datum A by more than ±0.1
Be flat within 0.1

Correct answer: Lie between two planes 0.1 apart and parallel to datum A

Parallelism creates a tolerance zone of two parallel planes separated by the tolerance value, both parallel to the referenced datum.

Question 19: When a perpendicularity tolerance is applied to a flat surface (not an axis), which modifier is NOT applicable?

Free State (F)
Maximum Material Condition (MMC) (Correct answer)
Projected Tolerance Zone (P)
All of the above are not applicable

Correct answer: Maximum Material Condition (MMC)

MMC and LMC modifiers apply only to features of size (axes or center planes), not to surfaces; perpendicularity on a flat surface cannot use MMC.

Question 20: A cylindricity tolerance of 0.03 mm means the entire cylindrical surface must fit between two coaxial cylinders whose radii differ by:

0.06 mm
0.015 mm
0.03 mm (Correct answer)
0.03 mm per side (0.06 total)

Correct answer: 0.03 mm

The cylindricity tolerance value of 0.03 mm equals the total radial difference between the two coaxial boundary cylinders.

Question 21: Which scenario correctly describes an angularity tolerance application?

A surface must be perpendicular to datum B within 0.05
A surface must be parallel to datum A within 0.05
A surface must be at 30° to datum C within a 0.05-wide zone (Correct answer)
A surface must be coplanar with datum D within 0.05

Correct answer: A surface must be at 30° to datum C within a 0.05-wide zone

Angularity controls a feature at a specified angle (other than 0° or 90°) to a datum, with the tolerance zone parallel to that angle.

GD&T Form and Orientation Tolerances

Which GD&T symbol is used to control the straightness of a surface element (line element) on a cylindrical part?

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