GD&T Tolerances & Fits in Engineering Drawings 4 — Questions and Answers
Question 1: A dimension shown as 62.50/62.45 on a drawing uses which tolerance expression method?
- Plus-minus bilateral
- Unilateral
- Limit dimensioning (Correct answer)
- Nominal with deviation
Correct answer: Limit dimensioning
Limit dimensioning directly states the maximum and minimum acceptable sizes without referencing a nominal value or deviation.
Question 2: If a shaft has a tolerance of 0.025 mm and the mating hole has a tolerance of 0.030 mm, what is the assembly tolerance?
- 0.005 mm
- 0.025 mm
- 0.030 mm
- 0.055 mm (Correct answer)
Correct answer: 0.055 mm
Assembly tolerance equals the sum of both component tolerances: 0.025 + 0.030 = 0.055 mm.
Question 3: In the shaft-basis fit system, which letter designates the reference shaft with zero fundamental deviation?
- H
- h (Correct answer)
- A
- a
Correct answer: h
In the shaft-basis system, 'h' designates the reference shaft whose upper deviation is zero.
Question 4: Which statement correctly describes 'least material condition' (LMC) for an external feature (shaft)?
- The shaft is at maximum diameter
- The shaft is at minimum diameter (Correct answer)
- The shaft has maximum surface roughness
- The shaft is at nominal diameter
Correct answer: The shaft is at minimum diameter
LMC for an external feature (shaft) occurs at its smallest permissible diameter, where the least material is present.
Question 5: A clearance fit specified as H8/f7 compared to H7/f6 would generally have:
- Tighter tolerances on both parts
- Larger tolerances and more clearance variation (Correct answer)
- The same clearance range
- Less total clearance
Correct answer: Larger tolerances and more clearance variation
Higher IT grade numbers (8 vs 7, 7 vs 6) mean wider tolerance zones, resulting in more variation in clearance across the assembly.
Question 6: A tolerance accumulation problem in a stack-up occurs when:
- All features share a common datum
- Individual tolerances of multiple parts combine to produce excessive assembly variation (Correct answer)
- A single part has multiple tolerance zones
- Bilateral tolerances are used instead of unilateral
Correct answer: Individual tolerances of multiple parts combine to produce excessive assembly variation
Tolerance stack-up occurs when multiple independent tolerances add together in a chain, potentially causing parts to not assemble correctly.
Question 7: According to ASME Y14.5, unless otherwise specified, general tolerances on drawings apply to:
- Only features with GD&T callouts
- All directly toleranced dimensions without specific tolerances (Correct answer)
- Only hole dimensions
- Only external features
Correct answer: All directly toleranced dimensions without specific tolerances
General tolerances (title block tolerances) apply to all dimensions that do not carry their own specific tolerance callout.
GD&T Tolerances & Fits in Engineering Drawings 4
A dimension shown as 62.50/62.45 on a drawing uses which tolerance expression method?