GD&T Tolerances & Fits in Engineering Drawings 3 — Questions and Answers
Question 1: A transition fit is best described as a fit where:
- Only clearance is possible
- Only interference is possible
- Either clearance or interference may result depending on actual sizes (Correct answer)
- The parts are always at nominal size
Correct answer: Either clearance or interference may result depending on actual sizes
A transition fit has tolerance zones that overlap, so actual assembled parts may have either a small clearance or a small interference.
Question 2: What is the tolerance grade (IT grade) system used to define?
- The type of fit (clearance, transition, interference)
- The magnitude of tolerance relative to nominal size (Correct answer)
- The surface finish of a feature
- The geometric tolerance of a feature
Correct answer: The magnitude of tolerance relative to nominal size
IT (International Tolerance) grades define the size of the tolerance zone; higher IT numbers indicate larger tolerances.
Question 3: A part drawing shows a dimension of 40.00 +0.05/−0.00. This is an example of which tolerance type?
- Bilateral tolerance
- Unilateral tolerance (plus only) (Correct answer)
- Limit dimensioning
- Equal bilateral tolerance
Correct answer: Unilateral tolerance (plus only)
When all tolerance variation is permitted in only one direction from nominal (here, only positive), it is a unilateral tolerance.
Question 4: When specifying a press fit for a steel pin in a housing, which fit category is most appropriate?
- H7/g6
- H7/f7
- H7/p6 (Correct answer)
- H7/h6
Correct answer: H7/p6
H7/p6 is a standard interference (press) fit designation where the shaft is larger than the hole at all conditions.
Question 5: What is meant by 'maximum material condition' (MMC) for a hole feature?
- The hole is at its largest diameter
- The hole is at its smallest diameter (Correct answer)
- The hole has the most roundness error
- The hole's position deviation is greatest
Correct answer: The hole is at its smallest diameter
For a hole, MMC corresponds to the smallest permissible diameter because at that size the part has the most material.
Question 6: The fundamental deviation in ISO limits and fits defines:
- The total tolerance range
- The position of the tolerance zone relative to nominal size (Correct answer)
- The surface quality required
- The inspection method to be used
Correct answer: The position of the tolerance zone relative to nominal size
The fundamental deviation (indicated by a letter) sets where the tolerance zone starts — how far it is offset from the nominal size.
Question 7: Which fit is typically used for bearings that must rotate freely with minimal play?
- H7/p6 (interference fit)
- H7/h6 (sliding fit)
- H7/f7 (running clearance fit) (Correct answer)
- H7/n6 (transition fit)
Correct answer: H7/f7 (running clearance fit)
H7/f7 provides a reliable running clearance suitable for bearings and rotating shafts that need free rotation with controlled play.
GD&T Tolerances & Fits in Engineering Drawings 3
A transition fit is best described as a fit where: