GD&T GD&T ASME Y14.5 Standards and Drawing Interpretation 1 — Questions and Answers
Question 1: Which standard governs GD&T practices in the United States?
- ASME Y14.5 (Correct answer)
- ISO 1101
- MIL-STD-8C
- ANSI B4.1
Correct answer: ASME Y14.5
ASME Y14.5, published by the American Society of Mechanical Engineers, is the U.S. standard defining GD&T symbols, rules, and practices.
Question 2: What does Rule #1 (the Envelope Principle) state in ASME Y14.5?
- A feature of size's surface must not violate a perfect-form envelope at MMC (Correct answer)
- All tolerances must be measured at LMC
- Geometric tolerances are mandatory on every drawing
- Datums must always be labeled in A-B-C order
Correct answer: A feature of size's surface must not violate a perfect-form envelope at MMC
Rule #1 requires that a feature of size controlled only by size tolerances must not violate a perfect-form (zero geometric error) boundary when the feature is at MMC.
Question 3: What is a 'feature of size' as defined by ASME Y14.5?
- A feature with directly opposed elements — such as a cylinder, hole, or two parallel surfaces — definable by a single size dimension (Correct answer)
- Any feature drawn on an engineering print
- A surface that has a datum callout
- A feature controlled exclusively by profile tolerance
Correct answer: A feature with directly opposed elements — such as a cylinder, hole, or two parallel surfaces — definable by a single size dimension
A feature of size has directly opposed surfaces or elements that can be measured across a single dimension, enabling MMC and LMC modifiers to apply.
Question 4: What does ASME Y14.5 Rule #2 establish?
- Unless otherwise specified, all geometric tolerances apply at RFS (Regardless of Feature Size) (Correct answer)
- Perfect form is required at LMC
- Datum references are mandatory for all tolerances
- Basic dimensions must appear in rectangular boxes
Correct answer: Unless otherwise specified, all geometric tolerances apply at RFS (Regardless of Feature Size)
Rule #2 makes RFS the default condition — if no modifier is shown in the feature control frame, the geometric tolerance applies at all feature sizes.
Question 5: What major new symbol was introduced in the ASME Y14.5-2018 revision?
- The Independent modifier (encircled I), which overrides Rule #1 for a specific feature (Correct answer)
- The Free State modifier
- The Projected Tolerance Zone symbol
- The Tangent Plane modifier
Correct answer: The Independent modifier (encircled I), which overrides Rule #1 for a specific feature
ASME Y14.5-2018 introduced the Independent modifier (Ⓘ), which explicitly releases a feature from Rule #1's perfect-form-at-MMC requirement.
Question 6: Under ASME Y14.5, what is the default geometric tolerance condition when no modifier is shown?
- Regardless of Feature Size (RFS) (Correct answer)
- Maximum Material Condition (MMC)
- Least Material Condition (LMC)
- Free State
Correct answer: Regardless of Feature Size (RFS)
Per Rule #2, RFS is the default — the geometric tolerance zone is fixed at the stated value regardless of the feature's actual produced size.
GD&T GD&T ASME Y14.5 Standards and Drawing Interpretation 1
Which standard governs GD&T practices in the United States?