GD&T Material Condition Modifiers — Questions and Answers

Question 1: A shaft has a true position tolerance of 0.2 MMC. At MMC the shaft diameter is 20.0 mm. If the shaft is produced at 19.8 mm, what is the total allowable position tolerance?

0.2 mm
0.4 mm (Correct answer)
0.6 mm
0.8 mm

Correct answer: 0.4 mm

The shaft has departed 0.2 mm from MMC, so the bonus tolerance (0.2) is added to the stated tolerance (0.2), giving 0.4 mm total.

Question 2: Which material condition modifier requires the tolerance zone to remain fixed regardless of the feature's actual size?

MMC
LMC
RFS (Correct answer)
Free State

Correct answer: RFS

RFS (Regardless of Feature Size) means the specified tolerance applies at every actual mating size with no bonus tolerance.

Question 3: On an internal feature (hole), the LMC condition corresponds to which of the following?

Largest allowable hole diameter
Smallest allowable hole diameter (Correct answer)
Virtual condition boundary
Midpoint of the tolerance range

Correct answer: Smallest allowable hole diameter

For a hole (internal feature), LMC is the smallest diameter because that represents the least material removed.

Question 4: The virtual condition of an external feature controlled at MMC is calculated as:

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

Correct answer: MMC size plus the geometric tolerance

For an external feature (e.g., shaft) at MMC, the virtual condition = MMC size + geometric tolerance, representing the worst-case boundary.

Question 5: Which modifier, when applied to a datum feature, allows the datum to shift as the feature departs from its referenced material condition?

Free State (F)
RFS
MMC on a datum reference (Correct answer)
Statistical Tolerance

Correct answer: MMC on a datum reference

Applying MMC (or LMC) to a datum reference in a feature control frame allows datum shift equal to the departure from that material condition.

Question 6: A hole has a diameter tolerance of 10.0–10.4 mm and a perpendicularity tolerance of 0.1 at MMC. What is the perpendicularity tolerance when the hole is produced at 10.4 mm (LMC)?

0.1 mm
0.3 mm
0.5 mm (Correct answer)
0.4 mm

Correct answer: 0.5 mm

At LMC (10.4 mm) the departure from MMC (10.0) is 0.4 mm, adding 0.4 bonus to the 0.1 stated tolerance gives 0.5 mm.

Question 7: Under ASME Y14.5-2009, when no material condition modifier is specified for a feature of size, which modifier is implied?

MMC
LMC
RFS (Correct answer)
Free State

Correct answer: RFS

ASME Y14.5-2009 established RFS as the default when no modifier symbol is shown in the feature control frame.

Question 8: The term 'resultant condition' for an internal feature controlled at MMC refers to:

The worst-case inner boundary considering both size and geometric tolerance (Correct answer)
The worst-case outer boundary considering both size and geometric tolerance
The virtual condition boundary
The boundary at RFS

Correct answer: The worst-case inner boundary considering both size and geometric tolerance

The resultant condition of an internal feature at MMC is the worst-case inner boundary = LMC size minus the maximum allowable tolerance.

Question 9: Which of the following GD&T tolerances is most commonly applied with an MMC modifier to take advantage of bonus tolerance for assembly purposes?

Flatness
Circularity
True Position (Correct answer)
Profile of a Surface

Correct answer: True Position

True position is most commonly modified with MMC because assembly clearance naturally increases when mating features depart from MMC.

Question 10: An LMC modifier is most useful for controlling which engineering concern?

Maximum interference in press-fit assemblies
Minimum wall thickness and edge distance (Correct answer)
Maximum bonus tolerance for assemblies
Datum feature shift for clearance fits

Correct answer: Minimum wall thickness and edge distance

LMC ensures minimum material (wall thickness, edge distance) is maintained, making it useful for structural or sealing concerns.

Question 11: A pin (external feature) has a size range of 9.9–10.0 mm. At MMC, the straightness tolerance is 0.05 mm. What is the maximum allowable straightness tolerance when the pin measures 9.9 mm?

0.05 mm
0.10 mm
0.15 mm (Correct answer)
0.20 mm

Correct answer: 0.15 mm

At 9.9 mm (LMC), departure from MMC is 0.1 mm; adding this bonus to 0.05 mm gives 0.15 mm total.

Question 12: Which boundary is established by the MMC size of an external feature PLUS its applicable geometric tolerance?

Inner boundary
Outer boundary / Virtual condition (Correct answer)
Resultant condition
Envelope principle boundary

Correct answer: Outer boundary / Virtual condition

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

Question 13: When an MMC modifier is applied to a tolerance of flatness, what happens?

Bonus tolerance is granted as the feature departs from MMC
The flatness zone expands but remains independent of size
It is invalid — flatness cannot use MMC (Correct answer)
The feature must be measured at MMC only

Correct answer: It is invalid — flatness cannot use MMC

Flatness is a surface form control that does not reference feature size, so applying MMC to flatness is not allowed per ASME Y14.5.

Question 14: Datum shift is analogous to bonus tolerance. Which statement correctly describes datum shift?

It is additional tolerance given to the controlled feature
It is the allowable movement of the true datum axis/plane due to the datum feature's departure from its referenced material condition (Correct answer)
It changes the MMC of the datum feature
It only applies when the datum is at RFS

Correct answer: It is the allowable movement of the true datum axis/plane due to the datum feature's departure from its referenced material condition

Datum shift is the permissible translation/rotation of the datum reference frame that occurs when the datum feature departs from its referenced material condition.

Question 15: Which symbol is used in a feature control frame to indicate the Maximum Material Condition modifier?

Ⓛ
Ⓜ (Correct answer)
Ⓢ
Ⓕ

Correct answer: Ⓜ

The circled M symbol (Ⓜ) is used in a feature control frame to designate the MMC modifier per ASME Y14.5.

Question 16: In a functional gauge for a position tolerance at MMC, the gauge pin diameter for a hole pattern would equal:

The LMC of the hole
The MMC of the hole minus the positional tolerance (Correct answer)
The MMC of the hole plus the positional tolerance
The virtual condition of the hole

Correct answer: The MMC of the hole minus the positional tolerance

The gauge pin diameter equals the virtual condition of the hole = MMC hole size minus the positional tolerance (for an internal feature).

Question 17: A feature control frame reads: position | 0.3Ⓜ | A | BⓂ. What does the Ⓜ on datum B indicate?

Bonus tolerance on the controlled feature
The controlled feature is at MMC
Datum shift is allowed based on datum B's departure from MMC (Correct answer)
Datum B must be inspected at MMC only

Correct answer: Datum shift is allowed based on datum B's departure from MMC

An MMC modifier on a datum reference (B Ⓜ) permits the datum reference frame to shift by the amount datum feature B departs from its MMC.

Question 18: Under the envelope principle (Rule #1), a feature of size must not violate its MMC perfect form boundary. Which material condition modifier explicitly overrides this rule?

RFS — it allows form error at any size
LMC — it sets the inner boundary
MMC applied to a straightness callout — it can allow the feature to exceed perfect form at MMC
Free State — it suspends Rule #1 for flexible parts (Correct answer)

Correct answer: Free State — it suspends Rule #1 for flexible parts

The Free State modifier (Ⓕ) suspends Rule #1 for non-rigid (flexible) parts measured in the free (unconstrained) state.

Question 19: Two mating parts use a clearance fit. The designer wants maximum allowable positional error when parts are easiest to assemble. Which modifier should be applied?

LMC
RFS
MMC (Correct answer)
Free State

Correct answer: MMC

MMC provides maximum bonus tolerance when parts are at their smallest shaft / largest hole (most clearance), maximizing allowed position error when assembly is easiest.

Question 20: A straightness callout of 0.1 Ⓜ is applied to a shaft with MMC of 25.0 mm and LMC of 24.6 mm. What is the maximum possible derived median line straightness tolerance?

0.1 mm
0.3 mm
0.5 mm (Correct answer)
0.6 mm

Correct answer: 0.5 mm

Maximum bonus = MMC (25.0) − LMC (24.6) = 0.4 mm; total max = 0.1 + 0.4 = 0.5 mm.

Question 21: Which of the following best defines 'actual mating size' as used when calculating bonus tolerance?

The average of the high and low measured diameters
The size of the largest perfect feature that will fit inside (or around) the produced feature (Correct answer)
The nominal size specified on the drawing
The size measured at the feature's midpoint

Correct answer: The size of the largest perfect feature that will fit inside (or around) the produced feature

Actual mating size is the size of the largest (for internal) or smallest (for external) perfect counterpart that fits the feature, used to determine departure from MMC.

GD&T Material Condition Modifiers

A shaft has a true position tolerance of 0.2 MMC.
At MMC the shaft diameter is 20.0 mm.
If the shaft is produced at 19.8 mm, what is the total allowable position tolerance?

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