GD&T GD&T ASME Y14.5 Standards and Drawing Interpretation 2 — Questions and Answers
Question 1: Reading a feature control frame left to right, what is the correct order of information?
- Geometric characteristic symbol, tolerance value with any modifiers, datum references in precedence order (Correct answer)
- Datum references, tolerance value, geometric characteristic
- Tolerance value, datums, geometric characteristic
- Part number, revision, tolerance
Correct answer: Geometric characteristic symbol, tolerance value with any modifiers, datum references in precedence order
A feature control frame is read: (1) what is being controlled (symbol), (2) how much (tolerance + modifiers), (3) relative to what (datum references A, B, C).
Question 2: What does the circled M symbol (ⓜ) in a feature control frame indicate?
- Maximum Material Condition — bonus tolerance applies as the feature departs from MMC (Correct answer)
- Minimum Material Condition
- Mean size condition
- The feature is measured at its midpoint
Correct answer: Maximum Material Condition — bonus tolerance applies as the feature departs from MMC
The encircled M specifies the MMC modifier, enabling bonus tolerance that grows as the actual feature size departs from its maximum material size.
Question 3: What is a basic dimension on an engineering drawing?
- A theoretically exact value, shown in a rectangular box, used to define the perfect geometry from which GD&T tolerance zones are measured (Correct answer)
- A reference-only dimension with no tolerance
- A dimension carrying the standard ±0.010 title-block tolerance
- A dimension used exclusively for functional gauging
Correct answer: A theoretically exact value, shown in a rectangular box, used to define the perfect geometry from which GD&T tolerance zones are measured
Basic dimensions (shown boxed) are perfect, zero-tolerance values that locate or orient GD&T tolerance zones; all tolerance is captured in the feature control frame, not the dimension itself.
Question 4: What does a reference dimension (shown in parentheses) mean on a drawing?
- It is provided for information only and is not used for inspection or part acceptance (Correct answer)
- It has the tightest tolerance on the drawing
- It is derived from a datum reference frame
- It is mandatory for functional gauging
Correct answer: It is provided for information only and is not used for inspection or part acceptance
Reference dimensions are informational, typically derived from other dimensions, and are never directly inspected or used to accept or reject a part.
Question 5: In a composite feature control frame with two segments, what does the upper segment control?
- The location of the entire pattern relative to the datum reference frame (Correct answer)
- The feature-to-feature relationship within the pattern
- The size tolerance of each feature
- The orientation of individual features only
Correct answer: The location of the entire pattern relative to the datum reference frame
The upper segment of a composite callout controls where the pattern is located relative to the specified datums, while the lower segment refines the within-pattern accuracy.
Question 6: When a feature control frame is attached to an extension line or dimension line (not a leader to the surface), what does this indicate?
- The tolerance applies to the derived axis or center plane of the feature (Correct answer)
- The tolerance applies directly to the surface
- The tolerance is informational only
- The tolerance applies to the entire part
Correct answer: The tolerance applies to the derived axis or center plane of the feature
Attaching a feature control frame to a dimension line means the tolerance controls the derived axis or center plane, not the physical surface itself.
GD&T GD&T ASME Y14.5 Standards and Drawing Interpretation 2
Reading a feature control frame left to right, what is the correct order of information?