GD&T Geometric Symbols & Notation 3 — Questions and Answers
Question 1: The GD&T symbol for 'Angularity' controls which characteristic?
- The orientation of a surface at a specified angle to a datum (Correct answer)
- The location of a surface relative to a datum
- The form of an angled surface independently of datums
- The runout of a feature at an angle
Correct answer: The orientation of a surface at a specified angle to a datum
Angularity is an orientation control that constrains a surface or axis to a specified angle (other than 0° or 90°) relative to a datum.
Question 2: What is the purpose of a 'projected tolerance zone' modifier (circled P) in GD&T?
- Extends the tolerance zone beyond the part surface to control mating part fit (Correct answer)
- Reduces the tolerance zone to a projected plane
- Indicates a statistical tolerance
- Specifies the tolerance in a cross-section view
Correct answer: Extends the tolerance zone beyond the part surface to control mating part fit
A projected tolerance zone extends the positional tolerance zone above the hole to control the orientation of a fastener as it protrudes into a mating part.
Question 3: Which feature control frame compartment always contains the geometric characteristic symbol?
- The first (leftmost) compartment (Correct answer)
- The second compartment
- The third compartment
- It can be in any compartment
Correct answer: The first (leftmost) compartment
Per ASME Y14.5, the first compartment of a feature control frame always contains the geometric characteristic symbol.
Question 4: What does 'BASIC' written below a dimension value indicate in a GD&T drawing?
- The dimension is theoretically exact and has no tolerance of its own (Correct answer)
- The dimension has a general tolerance applied
- The dimension is for reference only
- The dimension must be measured with a CMM
Correct answer: The dimension is theoretically exact and has no tolerance of its own
A basic dimension (shown in a box or labeled BASIC) is a theoretically exact value; its allowable variation is defined by the feature control frame tolerance.
Question 5: The GD&T symbol for 'Circular Runout' differs from 'Total Runout' in that:
- Circular runout is checked at individual cross-sections, while total runout accumulates across the entire surface (Correct answer)
- Circular runout controls the entire length, while total runout controls single circles
- Circular runout requires two datums, while total runout requires one
- Circular runout measures axial error only
Correct answer: Circular runout is checked at individual cross-sections, while total runout accumulates across the entire surface
Circular runout measures the variation at each individual circular cross-section independently, while total runout measures the combined variation over the entire surface.
Question 6: A 'datum target' symbol consists of:
- A circle divided by a horizontal line with the target number below and area size above (Correct answer)
- A triangle pointing to the surface
- A square with a datum letter inside
- A flag symbol on the leader line
Correct answer: A circle divided by a horizontal line with the target number below and area size above
Datum target symbols are circles split horizontally: the lower half contains the target identification (e.g., A1) and the upper half optionally contains the target area size.
Question 7: In GD&T, the 'Tangent Plane' modifier (circled T) means:
- The tolerance applies to a plane tangent to the high points of the surface (Correct answer)
- The tolerance applies to a tangential cross-section
- The feature must be tangent to a datum
- The tolerance is applied in a tangential direction only
Correct answer: The tolerance applies to a plane tangent to the high points of the surface
The tangent plane modifier specifies that the tolerance zone is evaluated using a plane contacting the high points of the surface rather than the entire surface.
GD&T Geometric Symbols & Notation 3
The GD&T symbol for 'Angularity' controls which characteristic?