Beginner’s Guide to Blueprint Reading

Learning to read blueprints can be hard. That’s why we’ve broken down the process into bite size chunks. All of the basic components of an engineering drawing are detailed below with links throughout to give you more info on each subject.

Use the table of contents below to jump straight to your topic of choice and if you don’t find what you are looking for please leave a comment at the bottom and we will tackle any blueprint related questions we may have missed.

Components of a drawing

Title block

title block example
Title block example

A blueprint title block contains the high-level identification information. The title block of a blueprint can vary quite a bit across different companies. In general, the title block can be found in the bottom right of the blueprint and will include the following:

  1. Drawing or part number and revision
  2. Part name
  3. Company name
  4. 1st or 3rd angle projection
  5. Scale

Tolerance block

tolerance block example
Tolerance block example

The tolerance block, sometimes referred to as the general tolerance block, is usually located in the bottom right or bottom middle section of the blueprint. The tolerance block identifies the tolerances associated with dimensions that are not directly listed on the drawing.

This can include items such as the blueprint dimensional units (imperial or metric) or surface roughness requirements.

Units of measurement

The units of the print are very important because there is a huge difference between 25.4mm and 25.4 inches. The measurement units will often be called out in the title block or tolerance block but occasionally will be in another section of the blueprint such as in the notes.

Angular units are important also but there is usually less confusion associated with them because decimal degrees and degrees, minutes, seconds are so different.

Types of projections

Projections are different ways of representing parts on a blueprint. Basically this means there are different methods of showing the same part.

1st angle projection, sometimes referred to as the European convention, is a method of displaying the various views of the part as if the part has been flipped to each side.

Notice how the car is flipped below in each view of a 1st angle projection blueprint.

1st angle projection car example
1st angle projection example - click to enlarge

3rd angle projection, the American convention, is a method of displaying the various views of the part as if the part is placed in a bowl and rolled in the bowl to the other views.

Notice how the car is flipped below in each view of a 3rd angle projection blueprint.

3rd angle projection example - click to enlarge

Projections can be hard to describe in words. Just remember that 1st angle projections are a flop method and 3rd angle projection is a roll method. 

Types of tolerances

There are multiple ways of tolerancing a dimension. Below are the ways of directly dimensioning a feature with standard tolerances. GD&T tolerances are a separate topic altogether.

Limit tolerances

limit tolerance example
Limit tolerance example

Limit tolerances list a range that the dimension must fall within. No calculation needed. Simply keep it between the numbers.

Unilateral tolerances

unilateral tolerance blueprint example
Unilateral tolerance example

Unilateral tolerances are given when the allowable variation is in a single direction such as the example below. In this example, the part cannot have a diameter that is over 6mm.

Bilateral tolerances

bilateral tolerance blueprint example
Bilateral tolerance example

Bilateral tolerances, often referred to as plus or minus tolerances, have a nominal size and a tolerance in the positive and negative directions. Often this tolerance will be equal in both directions, but it doesn’t have to be. Sometimes you will see bilateral tolerances that allow more variation in one direction.

Notes section

Notes on a blueprint can have a huge impact on the component requirements. The notes are often where surface treatment requirements such as heat treating, anodizing and other similar requirements are documented.

Literally anything can be listed in the notes section and the items listed can have a large bearing on the complexity of the part.

Pay attention to your notes section, there are often critically important features and characteristics relative to the part listed.

Symbols

A wide range of symbols are used to create engineering drawings. There are also specialty blueprint symbols associated with items such as welding or electronic components, but I will only be covering the standard blueprint symbols including those related to geometric dimensioning and tolerancing (GD&T).

Center lines

Center lines, such as the center of a thru hole are depicted on a drawing with long and short lines spaced alternately.

In the example below, the centerlines are shown as blue lines.

hidden and center line blueprint example
Center lines and hidden lines example

Hidden lines

To show features in a blueprint view that would not actually be visible, hidden lines are used. These hidden lines are show on a drawing as lines made of dashes.

In the example above, the hidden lines are shown as red lines

Diameters

Diameter Blueprint GD&T Symbol o with line through it
Diameter symbol

Diameters are round or cylindrical features. Features such as the outside diameter of a part and the size of a hole or counterbore are examples of diameters. They will be referenced using the diameter symbol shown below.

Countersinks

Countersink Blueprint GD&T Symbol two lines pointing down
Countersink symbol

Countersinks are a chamfer on a hole that allows a fastener such as a screw to sit flush or below the part surface. The blueprint symbol for a countersink is shown below.

countersink blueprint example
Countersink callout example

Counterbores

Counterbore Blueprint GD&T Symbol u shape
Counterbore symbol

A counterbore is a circular hole that is deep enough to allow the head of a fastener to be recessed. Counterbores will be shown on a blueprint with a diameter and depth symbol associated with them.

counterbore blueprint example
Counterbore callout example

Radii

Radius callout example

Radii show up on prints for many different reasons. The most common application of a radius is to specify the maximum radius allowed in the bottom of a slot or hole. They are frequently used as a form of edge relief similar to a chamfer. While these are the most common radius uses, radii can be dimensioned for all kinds of internal and external features.

When a radius smoothly blends into a surface, it will occasionally be called out as a full radius or full R. A full R callout does not change the way a radius is measured or add any additional requirements.

Holes

thru hole blueprint example

Holes are about as simple as they come. They come in two varieties, thru holes and blind holes. When shown on a drawing they will usually be referenced by their size and location to the center of the hole.

Datums

Datum Blueprint GD&T Symbol a in a box with arrow
Datum symbol

Datums are reference points for measurements and are utilized in many GD&T callouts. You will find datums shown on a drawing to identify the feature as a datum or as part of a GD&T callout in a feature control frame.

GD&T Symbols

gd&t symbols
gd&t symbols

Basic dimensions

Basic Dimension Blueprint GD&T Symbol dimension in a box
Basic dimension example

Basic dimensions are the theoretically perfect size or location of a part feature. The variation from this “perfect” size or location will be used to measure another characteristic of the part such as true position or profile. Basic dimensions do not have a tolerance themselves and instead are controlled by another GD&T callout.

Reference dimensions

Reference Dimension Blueprint GD&T Symbol dimension in parentheses
Reference dimension example

Reference dimensions are just what they sound like. They are placed on a print for reference only. They have no requirements associated with them and no tolerances either. They generally get used in one of two ways, they will be used to highlight something that might not be immediately clear without the reference dimension listed or they will be used to show the approximate dimension in another unit system (metric vs imperial units).

Chamfers

chamfer callout blueprint example
Chamfer callout example

Chamfers are used to remove the sharp edges of a part. This provides safety for both the part and the person using the part. Chamfers are frequently specified in many different places. They can be listed directly on the part, in the notes section or in the general tolerance block.

When the chamfers are small, at times they will be listed as a break edge.

Spotfaces

spotface example on mechanical blueprint drawing
Spotface callout example

Spotfaces are a small counterbore that is machined so that a fastener can sit flat on the part. They are essentially just shallow counterbores and will be dimensioned as such.

Bolt hole circles

basic dimensions for a bolt hole circle
Bolt hole circle callout example

A bolt hole circle will be shown on a print using multiple dimensions. This will include the size of the individual holes, the angle between the center of the bolt hole circle and the individual holes along with the size of the bolt hole circle itself.

Knurling

knurling blueprint callout examples
Knurling callout examples

Knurling is a textured pattern on a part. It is added for visual appeal or added grip. Knurls will be called out by the pitch, diameter, and type of knurling.

Surface finish/surface roughness

Surface Finish Blueprint GD&T Symbol check mark
Surface finish/roughness symbol

The surface finish quality is specified with the use of a check mark on the surface. The number above the start of the check is the required surface finish. If there are two numbers present, the surface roughness must fall within the range specified. If only one number is specified, the surface roughness must be less than or equal to the specified value.

Surface finish requirements are frequently specified directly on the applicable surfaces as well as in the notes section and general tolerance block.

Threads

Threads will be specified in either the ISO metric format or Unified National Coarse (UNC) thread format. This article clarifies the details of thread callouts.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Related articles

Complete Guide to Machining Blueprint Symbols

Common Blueprint Symbols

nominal size dimension with a tolerance

Nominal Size

In the example shown, 24 is the nominal size. It is the size that the tolerance envelope is based on. A reference/starting point.

plus or minus symbol

Plus or Minus

Plus or minus is the most common tolerance type. They are less common, but tolerances can be all negative, all positive or +/- with enequal sizes such as +3/-2.

45 degrees

Degree Symbol

The symbol used to callout angle requirements.

Reference dimensions are shown in parentheses. They are provided for informational use only. They are not size requirements but often help make the print easier to understand.

Symbols For Features

Radius Blueprint GD&T Symbol r

Radii

Half of a circle. The distance from the center of a circle to the edge.

Diameter Blueprint GD&T Symbol o with line through it

Diameters

The distance all the way across a circle. Two times the radius. This symbol gets used with other symbols as well such as counterbores, countersinks, and true position callouts.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth of

This symbol specifies the depth of a feature.

A counterbore is a flat bottomed, recessed hole.

Countersinks are a round, angled feature added to a hole. They are often used to allow a screw head or other fastener to sit flush with the surface.

A spotface is  a shallow counterbore that allows a fastener to sit straight. The symbol has a few variations that get used. Often the counterbore symbol portion is left out and the SF is used only.

Surface Finish Blueprint GD&T Symbol check mark

Surface Texture

A symbol for defining the surface finish of a part. There are many variations of the surface texture symbol but most often it is used with a microinch or micrometer value callout that specifies the roughness of a surface.

Symbols Used In GD&T Callouts

Basic dimensions represent a  theoretically perfect feature or size. They are shown enclosed in a box and are the basis for many GD&T callouts.

Datums are features that are used to locate a part for measurement. 

Feature control frames contain a geometric dimensioning and tolerance callout.

The example shown reads, the feature is perpendicular to within 0.001 to datum A.

GD&T Symbols

Symbols For Roundness

Circularity Blueprint GD&T Symbol circle

Circularity

Otherwise known as roundness. Circularity only applies at one location. You might check the roundness of a hole at a specific depth.

Cylindricity Blueprint GD&T Symbol circle with two lines coming off it

Cylindricity

Cylindricity is roundness but over all locations of a feature. Cylindricity of a hole would mean the hole must be round at all points.

Symbols Used for Flat Things

Straightness Blueprint GD&T Symbol line

Straightness

A straightforward requirement. The feature must be a straight line within the specified tolerance.

Flatness Blueprint GD&T Symbol parallelogram

Flatness

Similar to straightness but over a whole surface. The high and low of a surface must be within the specified tolerance of each other.

Symbols Used to Control Angles

Perpendicularity Blueprint GD&T Symbol two lines perpendicular to each other

Perpendicularity

Two features must be 90 degrees to each other.

Parallelism Blueprint GD&T Symbol two parallel lines

Parallelism

Two features must run together (180 degrees to each other).

Angularity Blueprint GD&T Symbol two lines at an angle

Angularity

Angularity is used when two features must be have a specific angle between them and the angle between the features is not 90 or 180 degrees.

Symbols Used for Profile

Profile of a Line Blueprint GD&T Symbol half circle not connected

Profile of a Line

Profile of a line controls the shape of a feature. Imagine it as controlling the outline of a feature.

Profile of a Surface Blueprint GD&T Symbol half circle

Profile of a Surface

Profile of a surface controls the shape of a feature but instead of controlling it in one location like profile of a line, it applies to the entire feature surface.

GD&T Symbols That Control Location of a Feature

True Position Blueprint GD&T Symbol target

True Position

Controls location of a feature based on the variation from the basic dimensions.

Concentricity Blueprint GD&T Symbol two concentric circles

Concentricity

A requirement that the centerline or axis of two features are located together. 

Symmetry Blueprint GD&T Symbol three lines

Symmetry

A requirement that a feature must be evenly located based on another feature. Centered based on a feature or location.

Runout Blueprint GD&T Symbol single arrow

Circular Runout

Controls how even a surface is when spun in a circle. 

Total Runout Blueprint GD&T Symbol two arrows

Total Runout

The same as circular runout but at all locations on the feature. Circular runout and total runout have a relationship similar to circularity and cylindricity.

Symbols That Change Tolerance

Maximum Material Condition Blueprint GD&T Symbol m in a circle

Maximum Material Condition

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Least Material Condition Blueprint GD&T Symbol l in a circle

Least Material Condition

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Projected Tolerance Zone Blueprint GD&T Symbol p in a circle

Projected Tolerance Zone

Used when a tolerance zone applies outside the boundaries of the physical part.

Regardless of Feature Size Blueprint GD&T Symbol s in a circle

Regardless of Feature Size

The tolerances do not change based on the size of the features. This is the default spec and any tolerance is assumed to be regardless of feature size even if the symbol is not used.

Unequally Disposed Profile Blueprint GD&T Symbol U in a circle

Unequally Disposed Tolerance Zone

Profile tolerance zones are normally centered on the nominal dimensions. When this is not the case, the unequally disposed tolerance symbol is used to move the tolerance zone based off the nominal dimensions.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Guide to Holes on Blueprints [Types, Symbols & Features]

Hole types

blind holes blueprint example
3 blind holes specified

Blind holes are holes that get drilled or milled to a specified depth but do not go all the way through the part.

thru hole blueprint example

Thru holes

Thru holes get drilled all the way through a part.

They can be specified as “thru” as shown in the example or the blueprint can make it clear visually that the hole goes all the way through the part.

cutaway example of blind and thru holes
3 blind holes and 1 thru hole

Blind holes vs thru holes

This picture of a part cut in half shows the difference between a thru hole and a blind hole. The three holes on the left are blind holes which do not break through to the other surface.

The thru hole on the right goes all the way through the part.

Symbols used to dimension holes

Diameter Blueprint GD&T Symbol o with line through it

Diameter

The diameter of the hole is the size. The diameter is the distance across the hole.

Radius Blueprint GD&T Symbol r

Radii

Less often, holes are specified with a radial dimension instead of a diameter. The radius is the distance from the center of the hole to the edge of the hole. This is equal to 1/2 of the diameter.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth

The depth of the hole is the distance that it is drilled to. 

Features associated with holes

Counterbore Blueprint GD&T Symbol u shape

Holes often get counterbores that allow a fastener such as a bolt head to be recessed. 

Holes with a counterbore will specify the size and depth of the hole as well as the size and depth of the counterbore.

Countersink Blueprint GD&T Symbol two lines pointing down

Countersinks get added to holes as either a way to specify a chamfer for protective purposes or to allow a fastener such as a screw head to be recessed.

Holes with a countersink will specify the size and depth of the hole as well as the size and angle of the countersink.

Spotface Blueprint GD&T Symbol SF in a u

Spotfaces are functionally no different than a counterbore. They are machined on a part to allow a fastener to sit flush, though not always completely recessed.

Holes with a spotface will specify the size and depth of the holes as well as the size and depth of the spotface.

Note: spotfaces are not always specified with the symbol shown. At times, they will only use the counterbore symbol and other times they will use the SF notation only.

Want to learn more?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

Geometric Dimensioning and Tolerancing Font – GD&T Keyboard Shortcuts

How to insert symbols into a Microsoft Word document

To insert GD&T symbols into Word, take note of the codes in the table below.

There are two types of symbols below. Some are alt codes (ALT+248) and some are Unicode characters (25B1 then ALT+X). Alt codes are entered by holding the ALT key and pressing the number code. Unicode characters are entered by typing the code and then holding the ALT key and pressing X.

How to insert GD&T symbols into a Microsoft Excel document

Not all the codes work in Excel. The ALT codes (ALT+248 style) work but the Unicode characters (25B1 then ALT+X style) do not. The best way to insert the GD&T symbols into Excel is to copy and paste the symbols.

GD&T Symbols Alt Codes

Symbol Name

Symbol

Code

Straightness

ALT+22

Flatness

25B1 - ALT+X

Circularity

25EF – ALT+X

Cylindricity

232D – ALT+X

Profile of a Line

ALT+239

Profile of a Surface

2313 – ALT+X

Angularity

2220 – ALT+X

Perpendicularity

ALT+8869

Parallelism

//

2225 – ALT+X

True Position

2316 – ALT+X

Concentricity

ALT + 10686

Symmetry

232F – ALT+X

Circular Runout

↗

2197 – ALT+X

Total Runout

2330 – ALT+X

Free state

ALT + 9403

Least material condition

ALT + 9409

Maximum material condition

Ⓜ

ALT + 9410

Projected tolerance zone

ALT + 9413

Regardless of feature size (RFS)

ALT + 9416

Tangent plane

ALT + 9417

Unequally disposed tolerance

ALT + 9418

Common Blueprint Symbol Alt Codes

Symbol Name

Symbol

Code

Degree

°

ALT + 248

Plus or Minus

±

ALT+241

Diameter

Ø

ALT+0216

Depth

ALT + 8615

Greater Than or Equal To

ALT+242

Less Than or Equal To

ALT+243

Counterbore

ALT+9012

Countersink

ALT+9013

Micro

µ

ALT+230

Surface Finish

2713 - ALT+X

Centerline

ALT + 8452

Want to learn more about GD&T?

GD&T is a complicated subject and understanding it correctly can be the difference between a perfect part and scrap.

The best way to learn GD&T is from experienced teachers who can break down the material into manageable pieces.

Luckily, we know someone.

And MachinistGuides.com readers get an exclusive discount on training!

GD&T Symbols – A Beginner’s Guide

Geometric dimensioning and tolerancing (GD&T) consists of a set of symbols and rules for applying them that communicates the requirements of an engineering blueprint.

GD&T controls variations of size, form, orientation, location and runout individually or in combination.

For help understanding even the most complex GD&T concepts, get comprehensive and practical training with an exclusive discount for MachinistGuides.com readers!

GD&T and Engineering Blueprint Symbols

True Position Blueprint GD&T Symbol target

True Position

Controls how far a feature can deviate from a given location.

Straightness Blueprint GD&T Symbol line

Straightness

A tolerance given that defines how far from a perfect line a feature can be. A 2D (line) requirement. 

Flatness Blueprint GD&T Symbol parallelogram

Flatness

Similar to straightness but the callout applies over the entire surface (plane).

Perpendicularity Blueprint GD&T Symbol two lines perpendicular to each other

Perpendicularity

Defines the maximum allowed deviation of a feature from 90°.

Parallelism Blueprint GD&T Symbol two parallel lines

Parallelism

Describes two features that are equally distanced from each other over their entire surfaces. 

Angularity Blueprint GD&T Symbol two lines at an angle

Angularity

Angularity is the allowed deviation from a theoretically perfect feature at a specified angle other than 90° or 180° from another feature.

Runout Blueprint GD&T Symbol single arrow

Circular Runout

Controls the runout of a rotated circular at any single location on the feature.

Total Runout Blueprint GD&T Symbol two arrows

Total Runout

Controls the runout of a rotated circular at all locations on the feature.

Profile of a Line Blueprint GD&T Symbol half circle not connected

Profile of a Line

A tolerance that identifies how close to a specified design a feature is at specific cross section.

Profile of a Surface Blueprint GD&T Symbol half circle

Profile of a Surface

A tolerance that identifies how close to a specified design a whole feature is.

Circularity Blueprint GD&T Symbol circle

Circularity

A tolerance that defines how round a feature must be at a single location.

Cylindricity Blueprint GD&T Symbol circle with two lines coming off it

Cylindricity

Similar to circularity but it applies over the entire cylinder instead of at a single point.

Concentricity Blueprint GD&T Symbol two concentric circles

Concentricity

A requirement that the centerline or axis of two features are located within a specified tolerance of each other.

Symmetry Blueprint GD&T Symbol three lines

Symmetry

Controls the location of a feature such as a slot to a datum.

Envelope Requirement Blueprint GD&T Symbol e in a circle

Envelope Requirement

Specifies that the feature may not exceed the minimum or maximum total size requirement. This applies at each cross section as well as over the entire feature.

Free State Blueprint GD&T Symbol f in a circle

Free State

For non-rigid parts, the specified GD&T requirements apply when the part is in a free state, where only the force of gravity is affecting the part.

Independency Blueprint GD&T Symbol i in a circle

Independency

Removes the form control for a feature. When independency is called out the feature size is controlled only by the attached requirement.

Least Material Condition Blueprint GD&T Symbol l in a circle

Least Material Condition (LMC)

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Maximum Material Condition Blueprint GD&T Symbol m in a circle

Maximum Material Condition (MMC)

A modifier that can give bonus tolerance based how close or far the features are from nominal size.

Projected Tolerance Zone Blueprint GD&T Symbol p in a circle

Projected Tolerance Zone

Used when a tolerance zone applies outside the boundaries of the physical part.

Regardless of Feature Size Blueprint GD&T Symbol s in a circle

Regardless of Feature Size (RFS)

The tolerances do not change based on the size of the features. This is an older symbol that is no longer used. This condition is assumed unless specified otherwise now.

Tangent Plane Blueprint GD&T Symbol t in a circle

Tangent Plane

Creates a plane based on the highest contact points of a feature. 

Unequally Disposed Profile Blueprint GD&T Symbol U in a circle

Unequally Disposed Profile

Profile tolerance zones are normally centered on the nominal dimensions. When this is not the case, the unequally disposed tolerance symbol is used to move the tolerance zone based off the nominal dimensions.

Continuous Feature Blueprint GD&T Symbol cf in a hexagon

Continuous Feature

Identifies two or more separate features that should be treated as one such as two planes separated by a keyway.

Statistical Tolerance Blueprint GD&T Symbol st in a hexagon

Statistical Tolerance

Specifies that statistical process controls can be used which may be more cost effective in some situations.

Slope Blueprint GD&T Symbol triangle

Slope

Identifies the rise over run of a feature. Shown as a ratio.

Conical Taper Blueprint GD&T Symbol triangle with line through it

Conical Taper

The ratio of size difference between two diameter sections.

Target Point Blueprint GD&T Symbol x

Datum Target Point

A single point that is to be used as a datum or as part of a datum.

A basic dimension is a theoretically exact dimension used to calculate GD&T tolerances. Shown enclosed in a box. Older blueprints may identify the feature with BSC instead.

Reference dimensions are shown in parentheses. They are not blueprint requirements. They are shown for informational purposes only.

Arc Length Blueprint GD&T Symbol number with an arc over it

Arc Length

Describes the length along an arc. Measures the distance around the outside of the arc. It is not a chord length.

Dimension Not to Scale Blueprint GD&T Symbol number with line underneath

Dimension Not to Scale

Features are not shown with the same relative scale for all features.

Square Blueprint GD&T Symbol

Square

Identifies a feature that has equal sizes for both length and width. 

Diameter Blueprint GD&T Symbol o with line through it

Diameter

The distance across the center of a circle. Two times the radius.

Radius Blueprint GD&T Symbol r

Radius

Half of the diameter. The distance from the center of a circle to the edge.

Spherical Diameter Blueprint GD&T Symbol s and o with a line through it

Spherical Diameter

A sphere or ball shaped feature specified by the diameter of the sphere.

Spherical Radius Blueprint GD&T Symbol SR

Spherical Radius

A sphere or ball shaped feature specified by the distance from the center of the sphere to the outside.

Controlled Radius Blueprint GD&T Symbol cr

Controlled Radius

A radius without flats or reversals.

Common Tolerance Zone Blueprint GD&T Symbol cz

Common Tolerance Zone

Identifies two or more separate features that should be treated as one such as two planes separated by a keyway.

Datum Blueprint GD&T Symbol a in a box with arrow

Datum

A feature which is used for location and measurement of other features.

A flat bottomed, recessed hole

A round, angled feature that allows a fastener such as a screw head to sit flush or below the surface.

A shallow counterbore. Shown as on simply SF on some blueprints.

Depth Blueprint GD&T Symbol line with arrow pointing down

Depth of

Identifies how deep a feature is. Commonly applied to holes, counterbores, etc.

Surface Finish Blueprint GD&T Symbol check mark

Surface Finish

Describes the surface texture or roughness of a surface. Can be specified as a max allowable roughness as  shown above or a range.

Places Blueprint GD&T Symbol 4x or 4 pl.

Number of Places

An identifier that lists the number of instances of a repeated feature.

All Around Blueprint GD&T Symbol a bent arrow with a circle at the bend

All Around

Identifies that a requirement applies around the entire perimeter (edge) of the part.

All Over Blueprint GD&T Symbol a bent arrow with two circles at the bend

All Over

Identifies that a requirement applies to all surfaces and features of a part.

Translation Blueprint GD&T Symbol triangle

Datum Translation

Allows the identified datum locating feature to be adjusted so that the feature is fully engaged.

Movable Datum Target Blueprint GD&T Symbol circle with A1 in it and lines coming off

Movable Datum Target

Identifies datum targets that may be shifted in a specified direction.

Dynamic Profile Blueprint GD&T Symbol triangle

Dynamic Profile Tolerance Zone

Controls the form of a feature. When the dynamic profile modifier is used, the profile callout does not control the size of the feature.

Datum Target Blueprint GD&T Symbol circle with diameter 3 in top and A1 in bottom half

Datum Target

The top section is the size and shape of the target area. The lower section lists the identifying letter and number.

From-To Blueprint GD&T Symbol arrow

From-To

Indicates a gradual change in tolerance between two points. The arrow points in the direction of the tolerance change.

Between Blueprint GD&T Symbol line with arrows on both ends

Between

Feature requirements apply between two specified locations.

Dimension Origin Blueprint GD&T Symbol cross hair with arrow

Dimension Origin

Indicates the feature that another feature should be measured from. Often used to indicate a measurement should be taken from a shorter surface.

Frequently asked questions

What does GD&T stand for?

GD&T stands for geometric dimensioning and tolerancing. 

What is GD&T used for?

GD&T is a way for engineers and designers to more accurately control features and tolerances on manufacturing drawings.

GD&T allows designers to place only the needed controls and tolerances on features which reduces cost and complexity of components.

GD&T is critical for designing mating parts and assemblies effectively. 

What are the 5 categories of GD&T callouts?

The categories of GD&T symbols are form, profile, orientation, location and runout.

In addition there are a large amount of supplementary symbols which are used to identify blueprint requirements.

What standards control GD&T use?

There are two main standards which govern the use of various GD&T symbols.

ASME Y14.5 is the main standard referenced and the current revision is the 2018 version of the standard. The standard is commonly referred to as ASME Y14.5-2018 or on occasion simply, Y14.5-2018.

There are multiple ISO standards which govern the use of symbols and their interpretation. ISO 8015, ISO 1101 and ISO 2768 are the three most common standards that detail GD&T use and interpretation.

How to read a GD&T callout

feature control frame description with parts identified

A GD&T callout comes in the form of a feature control frame.

Feature control frames are read from left to right.

It reads “Type of control” of “Tolerance” to Datum. It should be noted that if a diameter symbol is present before “Tolerance” then it indicates the shape of the tolerance zone is cylindrical.

Here are a couple examples with description of how to read them:

true position callout

True position of 0.2 to datums A and B

perpendicularity callout example with feature control frame

Perpendicularity of 0.001 to datum A

What is the best way to learn GD&T?

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