GD&T Material Condition Modifiers 4 — Questions and Answers
Question 1: 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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 4
Which symbol is used in a feature control frame to indicate the Maximum Material Condition modifier?