# Limits, fits and tolerances viva questions and answers

## Q: What is a limit in engineering?

A: A limit is a specific value or range of values that defines the acceptable variation of a dimension in an engineering drawing or specification.

## Q: What is a fit in engineering?

A: A fit refers to the degree of tightness or looseness between two mating parts.

## Q: What is a tolerance in engineering?

A: A tolerance is the allowable variation of a dimension from its nominal or target value.

## Q: What are the different types of fits?

A: The different types of fits include clearance fit, interference fit, and transition fit.

## Q: What is a clearance fit?

A: A clearance fit is a fit where the maximum size of the mating part is smaller than the minimum size of the hole or cavity it is intended to fit into.

## Q: What is an interference fit?

A: An interference fit is a fit where the minimum size of the mating part is larger than the maximum size of the hole or cavity it is intended to fit into.

## Q: What is a transition fit?

A: A transition fit is a fit that falls between a clearance fit and an interference fit, where the maximum size of the mating part is equal to or slightly larger than the minimum size of the hole or cavity it is intended to fit into.

## Q: What are the advantages of using a clearance fit?

A: The advantages of using a clearance fit include ease of assembly and disassembly, lower manufacturing costs, and reduced risk of damage to the parts due to less stress during assembly.

## Q: What are the advantages of using an interference fit?

A: The advantages of using an interference fit include higher mechanical strength and stability, improved resistance to vibration and movement, and better alignment of the mating parts.

## Q: What is meant by tolerance stack-up?

A: Tolerance stack-up is the accumulation of all the individual tolerances of each dimension in a system, which can result in a variation of the final assembled product.

## Q: What is meant by GD&T?

A: GD&T stands for Geometric Dimensioning and Tolerancing, which is a system of symbols, rules, and definitions used in engineering drawings to specify the allowable variation of geometric features and relationships between them.

## Q: What is meant by surface finish?

A: Surface finish refers to the texture, roughness, or smoothness of a surface, which can affect the performance and appearance of a product. It is typically specified in terms of roughness average (Ra) or other parameters using a surface roughness symbol.

## Q: What is a feature control frame (FCF)?

A: A feature control frame (FCF) is a graphic symbol used in GD&T to specify the allowable variation of a geometric feature or relationship. It consists of a series of blocks that indicate the type of tolerance, the geometric characteristic, the tolerance value, the datum references, and other modifiers.

## Q: What is meant by a basic dimension in GD&T?

A: A basic dimension is a theoretical dimension that is used as a reference for other dimensions and tolerances. It is shown in a rectangular box on a GD&T drawing, and it does not include any tolerance or allowance.

## Q: What is meant by a positional tolerance in GD&T?

A: A positional tolerance is a type of GD&T tolerance that specifies the allowable deviation of a feature or a pattern of features from a specified position or orientation. It is expressed as a distance or an angle, and it can have one or more datum references.

## Q: What is meant by a concentricity tolerance in GD&T?

A: A concentricity tolerance is a type of GD&T tolerance that specifies the allowable deviation of a feature or a set of features from a true center point or axis. It is typically used for cylindrical or spherical features, and it can have one or more datum references.

## Q: What is meant by a runout tolerance in GD&T?

A: A runout tolerance is a type of GD&T tolerance that specifies the allowable deviation of a feature or a set of features from a true circular or cylindrical form. It is typically used for rotating parts or features, and it can have one or more datum references.

## Q: What is meant by a hole basis system in limits, fits, and tolerances?

A: A hole basis system is a system of fits and tolerances where the hole or the internal feature is used as a basis for defining the fit. The hole is assigned a basic size and a tolerance, and the shaft or the external feature is assigned a clearance, interference, or transition fit.

## Q: What is meant by a shaft basis system in limits, fits, and tolerances?

A: A shaft basis system is a system of fits and tolerances where the shaft or the external feature is used as a basis for defining the fit. The shaft is assigned a basic size and a tolerance, and the hole or the internal feature is assigned a clearance, interference, or transition fit.

## Q: What is meant by a bilateral tolerance in limits, fits, and tolerances?

A: A bilateral tolerance is a type of tolerance where the allowable variation is specified in both positive and negative directions from the nominal dimension. It is typically shown as a symmetrical tolerance zone on a drawing.

## Q: What is meant by a unilateral tolerance in limits, fits, and tolerances?

A: A unilateral tolerance is a type of tolerance where the allowable variation is specified in only one direction from the nominal dimension. It is typically shown as an asymmetric tolerance zone on a drawing, with the arrow pointing in the direction of the allowable deviation.

## Q: What is meant by a fit allowance in limits, fits, and tolerances?

A: A fit allowance is the intentional difference between the basic size of a mating part and the actual size of the feature it is intended to fit into. It is typically expressed as a positive or negative allowance, depending on whether the mating part is larger or smaller than the nominal dimension of the feature.

## Q: What is meant by clearance fit in limits, fits, and tolerances?

A: A clearance fit is a type of fit where there is intentional clearance or space between the mating parts, allowing for easy assembly and disassembly. In a clearance fit, the maximum size of the shaft is smaller than the minimum size of the hole, so there is a gap between the two parts.

# Q: What is meant by interference fit in limits, fits, and tolerances?

A: An interference fit is a type of fit where the mating parts are intentionally forced together with an interference or overlap. In an interference fit, the minimum size of the shaft is larger than the maximum size of the hole, so the two parts are pressed or pressed and heated together to create a secure fit.

## Q: What is meant by transition fit in limits, fits, and tolerances?

A: A transition fit is a type of fit where the mating parts have a combination of clearance and interference, depending on the actual sizes of the parts. In a transition fit, the maximum size of the shaft is slightly smaller than the minimum size of the hole, so the parts can be assembled with a slight interference or a slight clearance, depending on the actual sizes.

## Q: What is meant by a tolerance stack-up in GD&T?

A: A tolerance stack-up is the accumulation of tolerances in a series of mating parts or features, which can result in larger deviations than expected. A tolerance stack-up analysis is used to identify the sources of variation and to ensure that the overall tolerance is within the desired limits.

## Q: What is meant by a datum in GD&T?

A: A datum is a theoretical reference point, line, plane, or surface that is used to establish and control the location and orientation of other features on a part or assembly. A datum is shown on a GD&T drawing with a rectangular box and a letter or a symbol, and it is used to establish the datum reference frame.

## Q: What is meant by a datum reference frame in GD&T?

A: A datum reference frame is a set of three mutually perpendicular datums that are used to establish and control the location and orientation of other features on a part or assembly. The datum reference frame is established by selecting three datums from the part or assembly and specifying their order and orientation.

## Q: What is meant by a material condition modifier in GD&T?

A: A material condition modifier is a GD&T symbol or note that indicates the condition of the material that is used to measure the feature or the part. The material condition can be specified as maximum material condition (MMC), least material condition (LMC), or regardless of feature size (RFS), depending on the desired level of precision and the manufacturing process.

## Q: What is meant by maximum material condition (MMC) in GD&T?

A: Maximum material condition (MMC) is a material condition modifier in GD&T that indicates the feature or the part is at its maximum material limit. In other words, the feature or the part has the most material that it can have within the allowable tolerance zone. This condition is used to ensure the maximum fit or function of the feature or the part.

## Q: What is meant by least material condition (LMC) in GD&T?

A: Least material condition (LMC) is a material condition modifier in GD&T that indicates the feature or the part is at its minimum material limit. In other words, the feature or the part has the least amount of material that it can have within the allowable tolerance zone. This condition is used to ensure the minimum fit or function of the feature or the part.

## Q: What is meant by regardless of feature size (RFS) in GD&T?

A: Regardless of feature size (RFS) is a material condition modifier in GD&T that indicates that the size of the feature or the part does not affect the tolerance zone. In other words, the tolerance zone is always the same, regardless of whether the feature or the part is at its maximum or minimum material limit. This condition is used to simplify the design and manufacturing process.

## Q: What is meant by a datum target in GD&T?

A: A datum target is a combination of a datum feature and a geometric tolerance that is used to control the location and orientation of a feature on a part or assembly. The datum feature is used as a reference point or surface, and the geometric tolerance specifies the allowable deviation from the nominal location or orientation.

## Q: What is meant by a virtual condition in GD&T?

A: A virtual condition is a theoretical condition that assumes the part or feature is perfectly formed and has no variation. A virtual condition is used in GD&T to establish the ideal geometry and to ensure that the actual geometry is within the desired tolerance limits.

## Q: What is meant by a bonus tolerance in GD&T?

A: A bonus tolerance is an additional tolerance that is added to the basic tolerance to allow for easier manufacturing or assembly. A bonus tolerance is typically added when a feature or a part has a functional requirement that is more critical than the design intent, and it can be used to provide a margin of error in the manufacturing or assembly process.

## Q: What is meant by a tolerance zone in GD&T?

A: A tolerance zone is a three-dimensional space that represents the allowable deviation from the nominal geometry of a feature or a part. The tolerance zone is defined by the geometric tolerance and the datum references, and it is used to ensure that the actual geometry of the feature or the part is within the desired limits.