Symbols and Rules Flashcards

Which GD&T symbol is used to control the orientation of a surface relative to a datum plane without controlling its location?

Answer: Parallelism

Parallelism controls the orientation of a surface or axis to be parallel to a datum without specifying its exact location.

What does the 'S' modifier inside a feature control frame signify?

Answer: Spherical diameter

The 'S' prefix before a diameter symbol (Sø) indicates a spherical diameter in GD&T.

Rule #2 in ASME Y14.5 states that unless otherwise specified, each tolerance of orientation, form, location, or runout applies to which condition?

Answer: Regardless of Feature Size (RFS)

Rule #2 (RFS) is the default condition — geometric tolerances apply regardless of actual feature size unless MMC or LMC is specified.

Which symbol in a feature control frame indicates that a tolerance applies to the full surface profile, including both sides of the tolerance zone equally?

Answer: Equal bilateral profile (no modifier)

A profile tolerance with no modifier defaults to equal bilateral disposition, split equally inside and outside the true profile.

The 'all around' symbol on a leader line in a profile tolerance callout is represented by:

Answer: A circle at the bend of the leader line

A circle placed at the junction of the leader line and the reference line indicates that the profile tolerance applies all around the cross-section.

In GD&T, what is the purpose of the datum feature symbol (a rectangle with a triangle)?

Answer: To identify a feature that serves as an origin for measurements

The datum feature symbol identifies physical features on a part that establish the coordinate system used for measurements and inspections.

Which of the following GD&T symbols controls both the form and the orientation of a surface with respect to a datum?

Answer: Angularity

Angularity controls the orientation of a surface or axis at a specified angle to a datum, inherently also controlling form within the tolerance zone.

What does the 'free state' symbol (circle with the letter F) indicate in a GD&T callout?

Answer: The tolerance applies after release from manufacturing fixturing

The free state modifier indicates that the geometric tolerance applies to the part in its unconstrained, free state — not held in a fixture.

A profile of a line tolerance differs from a profile of a surface tolerance in that it:

Answer: Controls only a cross-sectional slice at any given location

Profile of a line controls the shape of a cross-sectional profile at individual cross-sections, while profile of a surface controls the complete 3D form.

In a feature control frame, the compartment immediately following the tolerance value compartment contains:

Answer: The primary datum reference

After the tolerance value (and any modifier on it), the next compartments list datum references in order: primary, secondary, then tertiary.

Which symbol, when placed below a feature control frame, indicates that the tolerance applies to the entire length or surface — not per unit?

Answer: No additional symbol is needed; it applies to the entire extent by default

By default, a geometric tolerance applies to the full extent of the feature unless a 'per unit' basis is specified separately below the frame.

Which of the following is NOT a valid runout tolerance symbol in ASME Y14.5?

Answer: Total Runout of a Plane Surface

There is no separate GD&T symbol called 'Total Runout of a Plane Surface'; Total Runout (the arrow symbol) covers cylindrical and planar surfaces within one symbol.

The diameter symbol (ø) placed before a tolerance value in a feature control frame means the tolerance zone is:

Answer: Cylindrical

When ø precedes the tolerance value, the tolerance zone is a cylinder of that diameter surrounding the true axis or center.

According to ASME Y14.5, which rule governs the relationship between size tolerance and form tolerance for an individual feature of size?

Answer: Rule #1 (Envelope Principle)

Rule #1 (the Envelope Principle) states that the form of an individual feature of size must be within a perfect geometric envelope at MMC.

A 'basic dimension' in GD&T is identified on a drawing by:

Answer: Enclosing the value in a rectangular box

Basic dimensions are shown enclosed in a rectangular box and represent the exact theoretically perfect value from which toleranced dimensions are measured.

What is the function of the 'tangent plane' modifier (T in a circle) in a GD&T callout?

Answer: The tolerance applies to a plane contacting the high points of the surface

The tangent plane modifier means the tolerance controls the orientation of a tangent plane that contacts the high points of the surface, not the entire surface form.

Which GD&T characteristic uses two coaxial cylinders as its tolerance zone?

Answer: Cylindricity

Cylindricity requires all points of a cylindrical surface to lie within two coaxial cylinders separated by the specified tolerance.

The 'projected tolerance zone' symbol (P in a circle) is most commonly applied to:

Answer: Threaded holes or press-fit pins to control mating part interference

Projected tolerance zones extend the position tolerance above a hole to the height of the mating pin or fastener, preventing interference during assembly.

In GD&T, the term 'virtual condition' for an external feature at MMC is calculated as:

Answer: MMC size plus the applicable geometric tolerance

For an external feature (shaft) at MMC, virtual condition equals the MMC size plus the geometric tolerance, representing the worst-case boundary.

Which symbol instructs the inspector to measure a feature while it is rotating about a datum axis?

Answer: Circular Runout or Total Runout

Both circular runout and total runout require the part to be rotated 360° about the datum axis while a fixed indicator records deviations.