The American Society of Mechanical Engineers (ASME) is a professional organization that develops and maintains a wide range of technical standards. One of the most well-known standards developed by ASME is the ASME Y14.5 standard, which covers geometric dimensioning and tolerancing (GD&T).

GD&T is a system for specifying the size, shape, and orientation of features on a part. It is used to ensure that parts fit together properly and function as intended. The ASME Y14.5 standard provides detailed guidelines for the use of GD&T and is used in many industries, including aerospace, automotive, and manufacturing.

The ASME Y14.5 standard is widely recognized as the primary GD&T standard in the United States and is often used in conjunction with other national and international standards. It is known for its comprehensive coverage of GD&T principles, including symbols and terms, tolerance zones, form tolerances, orientation tolerances, location tolerances, runout tolerances, datum reference frames, and applications of GD&T.

The ASME Y14.5 standard is regularly updated to reflect the latest developments in GD&T and to address the needs of different industries. It is an important resource for professionals working in fields related to design, manufacturing, and inspection, as it helps to ensure the consistent and predictable application of GD&T principles.

The modern ASME Y14.5 standard can trace its roots to the MIL-STD-8 military standard, which was published in 1949. However, it is the 1982 Y14.5 publication that is generally accepted as the first standard to fully incorporate GD&T. Since that time, the ASME Y14.5 standard has been updated in approximately 10-year intervals, with the most recent version being published in 2018.

The ASME Y14.5 standard is developed and maintained by the Y14 Engineering Product Definition and Related Documentation Practices committee within ASME. It is intended to provide uniformity in drawing specifications and interpretation, reducing guesswork throughout the manufacturing process. By improving the quality, lowering costs, and shortening deliveries wherever mechanical parts are designed or manufactured, the ASME Y14.5 standard aims to benefit a wide range of industries.

Scope 

ASME Series conventions 

The ASME Y14 series is a set of standards that govern the preparation and interpretation of technical drawings, models, and other engineering documentation. These standards cover a wide range of topics, from  dimensioning and tolerancing to drawing and model presentation. The ASME Y14 series is widely used in the United States and other countries, and its conventions have become the industry standard for engineering documentation. 

The ASME Y14 series is divided into several individual standards, each with its own focus and purpose. Some of the most important standards in the series include: 

• ASME Y14.1 - Decimal Inch Drawing Sheet Size and Format: This standard establishes the size and format of engineering drawing sheets. 

• ASME Y14.2 - Line Conventions and Lettering: This standard defines the standard line types, symbols, and lettering used in technical drawings. 

• ASME Y14.3 - Multi- and Sectional View Drawings: This standard provides guidelines for creating and interpreting multiview and sectional view drawings. 

• ASME Y14.5 - Dimensioning and Tolerancing: This standard establishes a comprehensive system for specifying and tolerancing geometric features on engineering drawings. 

• ASME Y14.6 - Screw Thread Representation: This standard defines the symbols and conventions used to represent screw threads on technical drawings. 

• ASME Y14.8 - Castings, Forgings, and Molded Parts: This standard provides guidelines for the representation of castings, forgings, and molded parts on technical drawings. 

Each of these standards contains detailed guidelines and conventions for creating and interpreting technical drawings, models, and other engineering documentation. By following these standards, engineers, designers, and manufacturers can ensure that their documentation is clear, concise, and easily understood by others in their organization or industry. 

Fundamental rules 

ASME Y14.5 defines several fundamental rules for dimensioning and tolerancing. These rules help ensure that parts and assemblies are manufactured and assembled correctly, and that they will function as intended. 

Here are the main fundamental rules according to  ASME Y14.5: 

1. All dimensions and tolerances must be specified in accordance with the current ASME Y14.5 standard. 

1. Dimensions and tolerances must be applicable to the feature being specified. 

1. Dimensions and tolerances must be complete and unambiguous. 

1. Dimensions and tolerances must be specified in a way that ensures functional requirements are met. 

1. The specified tolerances must be sufficient for the intended function of the part or assembly. 

1. Geometric tolerances must be applied to features only when necessary. 

1. The specification of datum features and datum references must be consistent with the functional requirements of the part or assembly. 

1. Tolerances must be applied to features in a way that minimizes cost and complexity while still meeting functional requirements. 

By following these fundamental rules, designers and engineers can ensure that parts and assemblies are manufactured and assembled correctly, and that they will function as intended. 

 
Units of measure 

According to ASME Y14.5, it is essential to know the units of measure that are being used to dimension and tolerance the features of a part. The use of appropriate units of measure ensures that the part is produced to the correct size and that the tolerances are applied correctly. 

ASME Y14.5 recommends using the International System of Units (SI) as the primary system of units for dimensioning and tolerancing. However, other systems of units may be used as long as they are clearly indicated on the drawing. 

It is important to note that the use of different units of measure on a single drawing can lead to errors and confusion. Therefore, it is recommended to use a single system of units throughout the entire drawing. 

In addition, ASME Y14.5 specifies rules for rounding off dimensions and tolerances that depend on the units of measure used. These rules ensure that the tolerances are appropriate for the size of the part and that the dimensions and tolerances are consistent with each other. 

Types of dimensioning 

According to ASME Y14.5, there are four types of dimensioning: 

Size dimensioning: Size dimensioning refers to indicating the size of a feature or part using dimensions. 

Location dimensioning: Location dimensioning refers to indicating the location of features or parts relative to a datum or a reference point. 

Geometric dimensioning: Geometric dimensioning is a system of dimensioning that uses symbols and feature control frames to specify geometric tolerances on parts. 

Angular dimensioning: Angular dimensioning refers to indicating the angle between two features or parts. 

2. General Tolerancing and Related Principles 

Section 2 of ASME Y14.5 covers General Tolerancing and Related Principles. In this section, there are several concepts discussed that are crucial for engineering design and manufacturing. In this article, we will discuss all these concepts in detail. 

2.1 General: 

The general section of Section 2 of ASME Y14.5 provides a broad overview of the tolerancing principles and practices. It defines the terms used in the standard and describes the objectives of tolerancing. It also explains the role of tolerancing in the design process and its significance in ensuring the interchangeability of parts. 

2.2 Direct Tolerancing Methods: 

Direct tolerancing methods refer to the methods used to specify tolerances on the dimensions of a part directly. These methods include bilateral and unilateral tolerancing, where a tolerance is specified as a plus/minus value or only as a positive or negative value, respectively. Another method is limit dimensioning, where the tolerance is specified by two limit dimensions that define the acceptable range of sizes. 

2.3 Tolerance Expression: Tolerance expression refers to the way tolerances are specified on engineering drawings. There are various methods of tolerance expression, such as limit dimensioning, geometric tolerancing, and position tolerancing. Limit dimensioning uses two limit dimensions to specify the acceptable range of sizes, while geometric tolerancing and position tolerancing use symbols and feature control frames to specify tolerances. 

2.4 Interpretation of Limits: Interpretation of limits refers to the way limits are interpreted on engineering drawings. Limits of size define the maximum and minimum acceptable sizes of a feature. The interpretation of these limits is dependent on the feature's actual size and the method of tolerance expression used. 

2.5 Single Limits: Single limits are used to specify a tolerance on a dimension by specifying only the maximum or minimum limit of the acceptable range of sizes. This method is used for features where only one limit is critical. 

2.6 Tolerance Accumulation: Tolerance accumulation refers to the accumulation of tolerances on multiple features. When two or more features are in close proximity to each other, the tolerance on one feature may affect the tolerance on the other feature. It is important to consider tolerance accumulation when specifying tolerances to ensure that the parts will fit and function correctly. 

2.7 Limits of Size: Limits of size define the maximum and minimum acceptable sizes of a feature. The interpretation of these limits is dependent on the feature's actual size and the method of tolerance expression used. 

2.8 Applicability of Modifiers on Geometric Tolerance Values and Datum Feature References: Modifiers are symbols used in geometric tolerancing to modify the tolerance zone's shape or size. These modifiers affect the tolerance values and datum feature references. It is essential to understand the applicability of modifiers to ensure that the tolerances are correctly specified. 

2.9 Screw Threads: Screw threads are used in mechanical systems to transmit motion or force. They have specific tolerances that need to be specified correctly to ensure the interchangeability of parts. Section 2.9 of ASME Y14.5 covers the tolerancing of screw threads. 

2.10 Gears and Splines: Gears and splines are used in mechanical systems to transmit motion or force. They have specific tolerances that need to be specified correctly to ensure the interchangeability of parts. Section 2.10 of ASME Y14.5 covers the tolerancing of gears and splines. 

2.11 Boundary Conditions: Boundary conditions refer to the specific requirements of a part's form, fit, and function. They are essential to specify accurately to ensure the part's proper function. 

2.12 Angular Surfaces: Angular surfaces refer to surfaces that are not perpendicular or parallel to the primary datum. The use of basic dimensions and feature control frames can be used to control the angular orientation of these surfaces. 

2.13 Conical Tapers: Conical tapers refer to features that have a gradual change in diameter over a given length. The use of basic dimensions and feature control frames can be used to control the taper angle and length of the feature. 

2.14 Flat Tapers: Flat tapers refer to features that have a gradual change in thickness over a given length. The use of basic dimensions and feature control frames can be used to control the taper angle 

2.15 Radius: 

Another important concept discussed in Section 2 of ASME Y14.5 is the use of radius dimensions. A radius is a curved feature that is defined by its center point and its radius value. Radius dimensions can be used to define the shape and size of a curve, such as the inside or outside of a circular object. 

In ASME Y14.5, there are several rules that apply to the dimensioning of radius features. For example, the dimension should be placed at the center of the arc, and the center point should be clearly indicated. Additionally, the dimension line should not cross the arc, and the leader line should be directed to the center of the arc. 

The standard also provides guidance on how to specify the tolerance for a radius dimension. This can be done using a plus/minus tolerance or a bilateral tolerance. The tolerance value should be based on the application of the part and the required level of accuracy. 

2.16 Tangent Plane: 

In ASME Y14.5, the concept of tangent planes is also discussed in Section 2. A tangent plane is a flat surface that touches a curved surface at a single point, without intersecting it. Tangent planes can be used to define the position and orientation of a curved feature, such as the surface of a cylinder or cone. 

When dimensioning tangent planes, it is important to clearly indicate the point of tangency and the orientation of the plane. The standard also provides guidance on how to specify the tolerance for a tangent plane. This can be done using a plus/minus tolerance or a bilateral tolerance, depending on the application of the part and the required level of accuracy. 

In addition, ASME Y14.5 provides rules for the use of tangent planes in conjunction with other geometric features, such as datum features and geometric tolerances. By properly dimensioning tangent planes and applying the appropriate tolerances, designers and engineers can ensure that curved features are manufactured to the required level of accuracy and functionality. 

2.17 Statistical Tolerancing 

Statistical tolerancing, also known as statistical process control (SPC), is a method of controlling the variability of a product or process using statistical methods. In ASME Y14.5, statistical tolerancing is used to define limits for features that cannot be precisely controlled, such as surface finish or material thickness. 

Statistical tolerancing involves setting up control limits based on the mean and standard deviation of a set of measurements. These limits can then be used to determine if a product or process is within acceptable levels of variability. 

To use statistical tolerancing, it is necessary to collect data on the feature in question and calculate its mean and standard deviation. The control limits are then established based on the desired level of control and the variation in the data. 

Section 3 Symbology 

Section 3 of ASME Y14.5 covers the symbology used in dimensioning and tolerancing. Here are the details about the different points of Section 3: 

3.1 General: The General point of Section 3 defines the basic rules of dimensioning and tolerancing symbology. This includes the use of feature control frames, geometric tolerances, datum references, and notes to supplement symbols. The purpose of this section is to establish a clear and consistent means of communication between the designer, the manufacturer, and the inspector. 

3.2 Use of Notes to Supplement Symbols: This point explains the use of notes on a drawing to provide additional information about the features being dimensioned. Notes may be used to define specific requirements, indicate critical dimensions, or provide explanations for non-standard tolerances. 

3.3 Symbol Construction: The third point of Section 3 explains how to construct dimensioning and tolerancing symbols, including the use of leader lines, arrows, and geometric tolerance symbols. It also covers the use of reference symbols, such as diameter and radius symbols, and the placement of symbols with respect to the features being dimensioned. 

3.4 Feature Control Frame Symbols: This point covers the construction and placement of feature control frames, which are used to specify geometric tolerances on a drawing. It explains the various types of feature control frames, including composite, individual, and multiple-segment frames. 

3.5 Feature Control Frame Placement: This point explains where feature control frames should be placed on a drawing, and how they should be oriented with respect to the features being dimensioned. It also covers the use of datum feature symbols and the relationship between datum features and geometric tolerances. 

3.6 Definition of the Tolerance Zone: The sixth point of Section 3 defines the tolerance zone for each type of geometric tolerance. The tolerance zone is the three-dimensional space within which the feature or features being dimensioned must lie in order to be within tolerance. 

3.7 Tabulated Tolerances: The final point of Section 3 covers the use of tabulated tolerances, which are used to specify tolerances for features that are too numerous or too small to be dimensioned individually. It explains how to construct a tabulated tolerance, and how to specify the number of features that are covered by the tolerance. 

Section 4 of ASME Y14.5 covers Datum Reference Frames (DRF) and Related Principles. Datum reference frames are used to establish a three-dimensional coordinate system that helps locate features and control part orientation during manufacturing and inspection. The following are the main points discussed in this section: 

Section 4 Datum Reference Frames 

4.1 General: This section provides an overview of the importance of datum reference frames and the principles used in establishing them. It highlights the need for a well-defined DRF to ensure that parts are manufactured and inspected consistently. 

4.2 Degrees of Freedom: Degrees of freedom refer to the number of ways a part can move or rotate. This section discusses the six degrees of freedom and how they relate to a DRF. The six degrees of freedom are three linear motions (x, y, and z) and three rotational motions (pitch, yaw, and roll). 

4.3 Degrees of Freedom Constrained by Primary Datum Features Regardless of Material Boundary: This section explains how primary datum features can be used to constrain degrees of freedom, regardless of the material boundary. The primary datum feature is the first feature that makes contact with the datum reference frame during the manufacturing and inspection process. 

4.4 Constraining Degrees of Freedom of a Part: This section explains how secondary and tertiary datum features can be used to constrain the remaining degrees of freedom of a part. It also discusses the importance of choosing datum features that are stable and easy to locate during the manufacturing and inspection process. 

4.5 Datum Feature Simulator: Datum feature simulators are used to simulate the presence of a datum feature for the purpose of inspection. This section discusses the different types of datum feature simulators, including theoretical and physical simulators. 

4.6 Theoretical and Physical Application of Datum Feature Simulators: This section discusses the theoretical and physical application of datum feature simulators. Theoretical simulators are used to define the DRF, while physical simulators are used for inspection purposes. 

4.7 Datum Reference Frame: This section discusses the different types of datum reference frames, including single datum, compound datum, and datum target reference frames. It also explains how to establish the DRF and the importance of following an order of precedence when selecting datum features. 

4.8  Datum Features: 

Datum features are used in engineering drawings to define a reference coordinate system for measuring and controlling geometric features of a part. The datum features are the surfaces, points, or axes that are used to establish the datum reference frame. Datum features can be either primary or secondary, depending on their importance in controlling the geometry of the part. Primary datum features are the most critical features, and they are used to establish the primary datum reference frame. Secondary datum features are used to establish the secondary and tertiary datum reference frames. 

4.9 Datum Feature Controls: 

Datum feature controls are used to specify the allowable deviation from the true geometric characteristics of a datum feature. Datum feature controls include basic dimensions, geometric tolerances, and datum feature symbols. Basic dimensions define the nominal size of a feature, while geometric tolerances define the allowable deviation from the nominal size. Datum feature symbols are used to indicate the datum feature that is being controlled. 

4.10 Specifying Datum Features in an Order of Precedence: 

When specifying multiple datum features, it is important to establish an order of precedence. This means that the primary datum feature should be specified first, followed by the secondary datum feature, and so on. The order of precedence ensures that the datum reference frame is established correctly and that the tolerances on the part are controlled as intended. 

4.11 Establishing Datums: 

Establishing datums is a critical step in creating an accurate and reliable engineering drawing. Datum features are used to establish the datum reference frame, which is a three-dimensional coordinate system that is used to control the geometry of the part. The datum reference frame consists of three orthogonal planes that are defined by the primary, secondary, and tertiary datum features. The datum reference frame is used to establish the zero point for all measurements and tolerances on the part. 

4.12 Multiple Datum Features: 

Multiple datum features can be used to establish the datum reference frame. The number and type of datum features that are used depend on the geometry of the part and the desired level of control over the tolerances. It is important to specify the datum features in the correct order of precedence to ensure that the datum reference frame is established correctly. 

4.13 Mathematically Defined Surface: 

A mathematically defined surface is a surface that is defined by an equation or mathematical formula. Mathematically defined surfaces are used to establish the datum reference frame in certain applications, such as when the part geometry is complex or irregular. Mathematically defined surfaces are specified using a datum feature symbol that includes the mathematical formula. 

4.14 Multiple Datum Reference Frames: 

In some cases, multiple datum reference frames may be required to control the geometry of a part. This can occur when the part has multiple functional surfaces that require different levels of control. Multiple datum reference frames can be established using different datum features and datum planes. 

4.15 Functional Datum Features: 

Functional datum features are those features that are critical to the function of the part. These features are typically specified as primary datum features, and they are used to establish the primary datum reference frame. The tolerances on functional datum features are usually tighter than on other features of the part. 

4.16 Rotational Constraint About a Datum Axis or Point: 

Rotational constraint about a datum axis or point is used to control the orientation of a part relative to the datum reference frame. This can be important in applications where the orientation of the part is critical to its function. Rotational constraint can be specified using a datum feature symbol that includes the axis or point of rotation. 

4.17 Application of MMB, LMB, and RMB to Irregular Features of Size: 

When specifying irregular features of size, such as a curved surface or a non-cylindrical hole, it is important to indicate which side of the feature is the maximum material condition 

4.18 Datum Feature Selection Practical Application: In some cases, selecting a datum feature may be difficult, especially when multiple features are available. In such cases, the following factors should be considered to select the most suitable datum feature: 

The features' design function 

The features' form and orientation 

The location of the feature with respect to the part's function 

The feature's ease of measurement 

4.19 Simultaneous Requirements: Simultaneous requirements refer to the situation where a feature must meet multiple geometric tolerances simultaneously. In such cases, a composite control frame is used to indicate the multiple requirements. The composite control frame contains the geometric characteristic symbol and modifiers for each tolerance. 

4.20 Restrained Condition: A restrained condition occurs when a feature is prevented from moving or rotating by an external force. In such cases, the restrained condition is used to specify the feature's orientation and position with respect to the datum reference frame. 

4.21 Datum Reference Frame Identification: To prevent confusion, each datum reference frame should be identified with a unique uppercase letter. When multiple datum reference frames are used, each frame should be identified with a different letter. 

4.22 Customized Datum Reference Frame Construction: In some cases, a customized datum reference frame may be required to establish the required relationship between the part's features. Customized datum reference frames can be constructed using a combination of features and datums. 

4.23 Application of a Customized Datum Reference Frame: When using a customized datum reference frame, the frame's orientation and position must be defined explicitly to ensure that the part meets the required tolerances. 

4.24 Datum Targets: Datum targets are used to establish the location of a feature with respect to the datum reference frame. Datum targets are similar to datum features, but they do not constrain the degrees of freedom of the part. Datum targets are used to establish a location reference for inspection purposes. 

Section 5 Tolerances of Form 

5.1 General: Section 5 of ASME Y14.5 deals with tolerances of form. Form tolerances are used to control the shape, size, orientation, and location of a feature. 

5.2 Form Control: Form control is the use of form tolerances to specify the allowable deviation in the form of a feature. Form tolerances are used to control the form of features that cannot be controlled by size, position, or orientation tolerances alone. 

5.3 Specifying Form Tolerances: Form tolerances are specified using symbols that are placed in the feature control frame. The symbols used to specify form tolerances include straightness, flatness, circularity, cylindricity, and profile of a surface. These symbols are used to indicate the allowable deviation in form from the ideal or perfect shape. 

5.4 Form Tolerances: There are several types of form tolerances used to control the form of a feature. These include straightness, flatness, circularity, cylindricity, and profile of a surface. Straightness is used to control the straightness of a feature, while flatness is used to control the flatness of a surface. Circularity is used to control the roundness of a feature, and cylindricity is used to control the roundness and straightness of a feature. Profile of a surface is used to control the shape of a surface. 

5.5 Application of Free-State Symbol: The free-state symbol is used to indicate that the form tolerance applies to the feature in its free state or unloaded condition. This symbol is used to ensure that the form tolerance is not affected by any deformation or distortion that may occur during the manufacturing process. The free-state symbol is placed next to the form tolerance symbol in the feature control frame. 

Section 6  Tolerances of Orientation  

6.1 General: Section 6 of the ASME Y14.5 standard covers tolerances of orientation, which means the permissible variation in the orientation of features of size relative to a specified datum. The orientation tolerances apply to features such as planes, lines, and axes. 

6.2 Orientation Control: Orientation control specifies the permissible deviation from a specified orientation of a feature of size. The orientation is defined by a datum reference frame, and the permissible deviation is specified using orientation symbols. 

6.3 Orientation Symbols: Orientation symbols are used to specify the allowable orientation tolerance of a feature relative to the specified datum reference frame. The orientation symbols include: 

• Perpendicularity symbol (⊥): used to specify the allowable perpendicularity deviation of a feature relative to a datum plane. 

• Angularity symbol (∠): used to specify the allowable angular deviation of a feature relative to a datum plane or axis. 

• Parallelism symbol (‖): used to specify the allowable parallelism deviation of a feature relative to a datum plane or axis. 

• Concentricity symbol (◎): used to specify the allowable deviation of a feature's axis of rotation relative to a datum axis. 

6.4 Specifying Orientation Tolerances: Orientation tolerances are specified using the appropriate orientation symbols, along with the permissible deviation value in units such as degrees or millimeters. The symbol is placed in the feature control frame, which is used to specify all the geometric tolerances for the feature. 

6.5 Tangent Plane: The tangent plane is a feature of size that is specified using a tangent plane symbol. The symbol indicates the requirement for a specified tangent plane at a point or along a line on the surface of the part. The tangent plane is used to control the orientation of a surface or a line relative to a specified datum. 

6.6 Alternative Practice: Alternative practices for specifying orientation tolerances include using a coordinate measuring machine (CMM) or functional gauging. CMMs can measure the actual orientation of a feature relative to the datum and provide a numerical value for comparison to the specified tolerance. Functional gauging involves the use of specialized gauges to verify that the feature meets the specified orientation tolerance. 

Section 7 Tolerances of Location 

7.1 General: The tolerances of location specify the allowable deviation from nominal position of features on a part. It is the third category of tolerances described in ASME Y14.5, and it includes positional tolerances, pattern location, coaxial feature controls, and tolerancing for symmetrical relationships. 

7.2 Positional Tolerancing: Positional tolerancing is a method of specifying the allowable deviation from nominal position of a feature on a part. It is used when the location of the feature is critical to the function of the part. Positional tolerancing may be applied to features of size or to datums, and it may be specified as either a basic dimension or a datum feature. 

7.3 Positional Tolerancing Fundamentals: I: Positional tolerancing fundamentals include the concept of "true position," which is the exact location of a feature's center point, and the "tolerance zone," which is the area within which the feature's center point must fall. The tolerance zone is defined by a cylindrical boundary, the size of which is determined by the specified positional tolerance. The positional tolerance can be specified as a basic dimension or as a datum feature. 

7.4 Positional Tolerancing Fundamentals: II: Positional tolerancing fundamentals also include the use of a feature control frame (FCF) to specify the positional tolerance. The FCF includes a symbol that represents the tolerance type, a tolerance value, and datum references that establish the orientation and location of the tolerance zone. The tolerance value may be specified as either a plus/minus tolerance or as a diameter or radius. 

7.5 Pattern Location: Pattern location is a method of specifying the allowable deviation from nominal position of a pattern of features on a part. Pattern location may be specified using a rectangular coordinate system or a polar coordinate system. The FCF used to specify pattern location includes a pattern control modifier that indicates the type of pattern, such as circular or linear, and a pattern reference that establishes the orientation and location of the pattern. 

7.6 Coaxial Feature Controls: Coaxial feature controls are used to specify the allowable deviation from nominal position of two or more coaxial features on a part. The FCF used to specify coaxial feature controls includes a symbol that represents the tolerance type, a tolerance value, and datum references that establish the orientation and location of the tolerance zone. 

7.7 Tolerancing for Symmetrical Relationships: Tolerancing for symmetrical relationships is used to specify the allowable deviation from nominal position of features on a part that have symmetrical relationships. Symmetrical relationships may be specified using bilateral or unilateral tolerancing, and the FCF used to specify symmetrical tolerancing includes a symbol that represents the tolerance type, a tolerance value, and datum references that establish the orientation and location of the tolerance zone. 

Section 8 Tolerances of Profile 

Section 8 of the GD&T standard covers tolerances of profile. Here are the key points: 

8.1 General: This section provides an overview of profile tolerancing, which is used to control the shape of a feature, such as a surface or curve, and ensure that it falls within a specified tolerance zone. 

8.2 Profile: Profile tolerance is the amount of variation allowed in the shape of a feature. It is expressed as a distance or a percentage of the feature's size. 

8.3 Tolerance Zone Boundaries: The tolerance zone for profile tolerancing is defined by two boundary lines, the upper and lower limits, which are parallel to the true profile of the feature. These boundary lines can be flat, curved, or a combination of both. 

8.4 Profile Applications: Profile tolerancing is commonly used to control the shape of surfaces, curves, and other complex features. It is especially useful for ensuring that mating parts fit together properly and for controlling the shape of functional surfaces, such as sealing surfaces. 

8.5 Material Condition and Boundary Condition Modifiers as Related to Profile Controls: Material condition and boundary condition modifiers can be used with profile tolerancing to specify the conditions under which the feature's shape is to be evaluated. For example, the feature may need to be evaluated in a maximum material condition or a minimum material condition. 

8.6 Composite Profile: Composite profile tolerancing is used to control the shape of multiple features simultaneously. It is commonly used in applications where a series of features must fit together precisely, such as in automotive assembly. 

8.7 Multiple Single-Segment Profile Tolerancing: This method is used to apply multiple profile tolerances to different segments of a feature. For example, different tolerances might be applied to different sections of a complex curve. 

8.8 Combined Controls: Profile tolerancing can be combined with other types of tolerances, such as positional or angular tolerances, to provide a complete specification for a feature's shape, location, and orientation. 

Section 9 Tolerances of Runout 

Section 9 of the ASME Y14.5 standard covers tolerances of runout. The main points of this section are: 

9.1 General: This section provides an overview of tolerances of runout. 

9.2 Runout: Runout is defined as the total variation of a surface or feature in relation to a datum axis. 

9.3 Runout Tolerance: The runout tolerance specifies the amount of runout allowed and is specified as a perpendicular distance from the datum axis to the surface or feature being measured. 

9.4 Types of Runout Tolerances: There are two types of runout tolerances: circular runout and total runout. Circular runout controls the circularity of a surface or feature around its axis, while total runout controls the overall variation of a surface or feature in all directions. 

9.5 Application: Runout tolerances are typically applied to cylindrical features such as shafts, holes, and bearing surfaces. 

9.6 Specification: Runout tolerances are specified using a symbol that indicates the type of tolerance (circular or total), the datum axis, and the tolerance value. The tolerance value is usually expressed in units of length, such as inches or millimeters.