GD&T Tolerances & Fits in Engineering Drawings

Question 1

What does the symbol ⊗ represent in GD&T?

Accepted Answer

Location of a datum feature.

Answer

The symbol ⊗ (a circle with a cross inside) in GD&T is used to indicate a datum target point. Datum targets are specific points, lines, or areas on a part that are used to establish a datum reference frame when the entire surface is too complex or impractical to use as a datum. This ensures consistent and repeatable measurement and manufacturing.

Question 2

What does the fit symbol Ⓕ represent in GD&T?

Accepted Answer

The fit between two parts.

Answer

In GD&T, the fit symbol Ⓕ (a circle with an F inside) is used to specify the type of fit required between mating parts. This symbol is often accompanied by specific tolerance values and designations (e.g., RC for running clearance, FN for force fit) to clearly define the desired relationship and allowable interference or clearance between assembled components.

Question 3

What does the term 'clearance fit' refer to in GD&T?

Accepted Answer

A fit that allows for movement between parts.

Answer

A 'clearance fit' in GD&T refers to a condition where there is always a gap or space between mating parts when they are assembled, even at their worst-case material conditions. This type of fit is designed to allow for free movement, rotation, or sliding between components. It is suitable for applications where parts need to move relative to each other without binding.

Question 4

Which symbol in GD&T represents the concept of 'true position'?

Accepted Answer

⟘.

Answer

The symbol ⟘ is the standard GD&T symbol for 'position' or 'true position'. It indicates the allowable deviation of a feature's actual location from its theoretically exact true position relative to specified datums. This symbol is crucial for controlling the precise placement of features like holes, slots, or pins.

Question 5

What is the function of the 'maximum material condition' (MMC) symbol in GD&T?

Accepted Answer

To specify the limits of size for a part.

Answer

The Maximum Material Condition (MMC) symbol (Ⓜ) in GD&T indicates that a geometric tolerance applies when a feature of size contains the maximum amount of material within its dimensional limits (e.g., largest pin, smallest hole). This condition allows for additional tolerance (bonus tolerance) as the feature departs from MMC, effectively specifying the functional limits of size and form for mating parts to ensure interchangeability and proper assembly.

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

(GD&T) Geometric Dimensioning and Tolerancing Certification Practice Test

GD&T Tolerances & Fits in Engineering Drawings