GD&T Runout and Concentricity — Questions and Answers

Question 1: What is the key difference between circular runout and total runout?

Circular runout applies to a single cross-section while total runout applies along the entire surface (Correct answer)
Total runout only applies to flat faces while circular runout applies to cylinders
Circular runout requires a more expensive gauge than total runout
Total runout is always a tighter tolerance than circular runout

Correct answer: Circular runout applies to a single cross-section while total runout applies along the entire surface

Circular runout measures deviation at individual cross-sections, whereas total runout accumulates error across the entire length of the surface.

Question 2: When a runout tolerance is applied to a conical surface, what does the tolerance zone represent?

Two coaxial cylinders
Two parallel planes perpendicular to the axis
Two lines along the cone surface separated by the tolerance value (Correct answer)
A cylindrical zone centered on the datum axis

Correct answer: Two lines along the cone surface separated by the tolerance value

For conical surfaces, the runout tolerance zone consists of two lines on the cone surface separated by the tolerance value, measured perpendicular to the surface.

Question 3: A shaft has a total runout tolerance of 0.05 mm. During inspection, the FIM (Full Indicator Movement) reading is 0.04 mm. The part is:

Rejected because FIM must be exactly equal to the tolerance
Accepted because the FIM is within the 0.05 mm tolerance (Correct answer)
Rejected because total runout requires zero FIM
Accepted only if re-measured on a different datum

Correct answer: Accepted because the FIM is within the 0.05 mm tolerance

The part passes because the measured FIM of 0.04 mm is less than the specified total runout tolerance of 0.05 mm.

Question 4: Concentricity is most accurately described as a control of:

Surface elements relative to a datum axis
The median points of diametrically opposed surface elements relative to a datum axis (Correct answer)
The center of a circle relative to a datum plane
The axis of a cylinder relative to a datum surface

Correct answer: The median points of diametrically opposed surface elements relative to a datum axis

Concentricity controls the location of the derived median points of all diametrically opposed surface elements, not the surface itself.

Question 5: Which of the following characteristics makes concentricity difficult to verify?

It requires specialized runout equipment not commonly found in shops
It requires deriving median points from opposing surface elements rather than direct surface measurement (Correct answer)
It cannot be measured on a surface plate
It requires the part to be rotating during inspection

Correct answer: It requires deriving median points from opposing surface elements rather than direct surface measurement

Finding median points of diametrically opposed elements requires complex calculations, making concentricity verification more difficult than runout.

Question 6: A designer wants to control wobble of a rotating disk face. Which GD&T control is most appropriate?

Flatness
Circular runout applied to the face (Correct answer)
Concentricity
Parallelism

Correct answer: Circular runout applied to the face

Circular runout applied to a face (axial runout) directly controls wobble of a rotating surface relative to a datum axis.

Question 7: In GD&T, what does MMC (Maximum Material Condition) bonus tolerance apply to for runout callouts?

Runout tolerances can use MMC modifiers on the datum feature
MMC bonus tolerance is not applicable to runout tolerances (Correct answer)
Runout tolerances always use MMC on the controlled feature
MMC applies to runout only for external features

Correct answer: MMC bonus tolerance is not applicable to runout tolerances

Runout is a surface control and cannot use MMC or LMC modifiers because it applies directly to surfaces, not to axes or center planes.

Question 8: Which datum reference is required for a runout tolerance callout?

A datum plane only
A datum axis (Correct answer)
A datum point
No datum is required for runout

Correct answer: A datum axis

Runout tolerances always require a datum axis because the surface elements are measured relative to rotation about that axis.

Question 9: A cylindrical surface has a circular runout tolerance of 0.03 mm and is also controlled by a size tolerance of ±0.1 mm. Which statement is correct?

Runout automatically overrides the size tolerance
Both tolerances must independently be satisfied (Correct answer)
The size tolerance is irrelevant when runout is specified
Only the tighter of the two tolerances needs to be met

Correct answer: Both tolerances must independently be satisfied

Size and runout are independent controls; a feature must conform to both its size tolerance and its runout tolerance separately.

Question 10: Total runout when applied to a cylindrical surface simultaneously controls which combination of errors?

Straightness and roundness only
Cylindricity, coaxiality, and taper (Correct answer)
Parallelism and perpendicularity only
Position and angularity of the axis

Correct answer: Cylindricity, coaxiality, and taper

Total runout on a cylinder controls all surface variations including out-of-roundness, wobble, taper, waviness, and coaxiality errors.

Question 11: A part drawing shows a runout callout with two datum references (e.g., A-B). What does this typically indicate?

The datum axis is established by two datum features used together (Correct answer)
The runout is measured alternately from datum A then datum B
Only datum A is used; datum B is a backup
The tolerance applies to both surfaces simultaneously

Correct answer: The datum axis is established by two datum features used together

Two datum references for runout typically establish a common datum axis from two separate datum features used simultaneously.

Question 12: Why is symmetry sometimes used as an alternative to concentricity for symmetric features?

Symmetry is easier to apply to non-round features than concentricity (Correct answer)
Symmetry allows MMC modifiers while concentricity does not
Symmetry is cheaper to inspect than concentricity
Symmetry only applies to prismatic features while concentricity applies to round ones

Correct answer: Symmetry is easier to apply to non-round features than concentricity

Symmetry controls the median points of features relative to a datum plane, making it applicable to non-cylindrical symmetric features where concentricity is not appropriate.

Question 13: When inspecting total runout on a stepped shaft, how many dial indicator passes are required?

One pass across the entire controlled surface (Correct answer)
One pass per step, each reset to zero
Two passes — one clockwise, one counterclockwise
As many passes as there are diameter changes, averaged together

Correct answer: One pass across the entire controlled surface

Total runout requires the indicator to traverse the entire controlled surface in a single continuous sweep while the part rotates.

Question 14: A runout tolerance frame contains the symbol for circular runout and the value 0.02. Where is the leader arrow typically directed?

To the datum feature
To the surface being controlled (Correct answer)
To the center axis of the part
To the tolerance block in the title block

Correct answer: To the surface being controlled

The feature control frame leader arrow points to the surface being controlled by the runout tolerance, not the datum.

Question 15: What instrument is most commonly used to measure runout in a production environment?

Coordinate Measuring Machine (CMM) only
Dial test indicator (DTI) with the part rotating on centers or in a chuck (Correct answer)
Optical comparator
Thread plug gauge

Correct answer: Dial test indicator (DTI) with the part rotating on centers or in a chuck

A dial test indicator placed against the surface while the part rotates on centers or in a V-block is the standard production method for measuring runout.

Question 16: If a shaft is bent (curved axis), which runout measurement will show the largest FIM reading?

Circular runout at the midpoint
Total runout along the full length (Correct answer)
Circular runout at either end
Both circular and total will show identical readings

Correct answer: Total runout along the full length

Total runout captures all cumulative surface deviations including the effect of a bent axis along the entire length, giving the largest FIM reading.

Question 17: Concentricity is removed from ASME Y14.5-2018. What control replaces it for most design intents?

Runout
Symmetry
Position with median points notation
Coaxiality using position (Correct answer)

Correct answer: Coaxiality using position

ASME Y14.5-2018 removed concentricity and recommends using position applied to the axis (coaxiality) as a more verifiable replacement.

Question 18: A print specifies circular runout of 0.05 mm on a journal bearing surface. The measured FIM at one cross-section is 0.06 mm. What action should be taken?

Accept the part since one cross-section is not representative
Reject the part as it exceeds the specified tolerance (Correct answer)
Re-measure using total runout instead
Accept only if the average of all cross-sections is under 0.05 mm

Correct answer: Reject the part as it exceeds the specified tolerance

Circular runout must be within tolerance at every cross-section; a single cross-section exceeding 0.05 mm causes rejection.

Question 19: Which of the following best describes the tolerance zone for total runout on a cylindrical surface?

A series of concentric circles at each cross-section
Two coaxial cylinders with a radial distance equal to the tolerance value (Correct answer)
Two parallel planes perpendicular to the datum axis
A single cylinder centered on the actual axis

Correct answer: Two coaxial cylinders with a radial distance equal to the tolerance value

The total runout tolerance zone for a cylinder is defined by two coaxial cylinders, one inside the other, separated by the stated tolerance value.

Question 20: On a drawing, runout is specified with datum reference A, which is a short cylindrical feature. What concern might an inspector raise?

Short datum features can be less stable for establishing an accurate axis (Correct answer)
Runout cannot use cylindrical datums
Short datums require a higher tolerance value
The inspector must use CMM for short datum features

Correct answer: Short datum features can be less stable for establishing an accurate axis

Short datum features provide limited constraint for establishing a stable axis, which can introduce uncertainty in the runout measurement.

Question 21: When a face and diameter are used together as compound datums for runout, what geometric relationship do they establish?

A datum axis perpendicular to a datum plane at a specific point (Correct answer)
Two parallel planes
A floating axis with no angular constraint
A datum center point only

Correct answer: A datum axis perpendicular to a datum plane at a specific point

A compound datum combining a face and diameter establishes a datum axis that is perpendicular to the face and coincident with the diameter's axis.

GD&T Runout and Concentricity

What is the key difference between circular runout and total runout?

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