3-2-1 Rule

A rule that defines the minimum number of contact points necessary to properly locate a part within the datum reference frame. The primary datum requires three points, the secondary datum two points, and the tertiary datum one point.

actual mating envelope

AME. A geometrically perfect shape that is a "best fit" around a feature. The AME is the smallest possible cylinder contacting a shaft at its highest points or the largest possible cylinder contacting a hole at its highest points.

angles

A shape formed by two lines that intersect or two rays or line segments sharing a common endpoint. Angles are formed when a section of a part feature has one vertex and two sides.

auxiliary views

A print view that presents illustrations showing a part at various angles other than a straight-on perspective. Auxiliary views provide a fuller picture of an angled side that cannot be fully represented with a basic orthographic view.

axis

An imaginary straight line that lies in the center of an object. When a cylindrical surface forms a feature of size in GD&T, it establishes the axis of that cylinder.

base units

A unit of measurement that can be determined by taking one measurement without having to combine any other measurement. Length, mass, and temperature are examples of base units.

basic dimension

A dimension that is theoretically perfect. A basic dimension has no direct tolerance and is denoted on a GD&T blueprint as a number enclosed in a rectangular box.

bilateral tolerances

A tolerancing method using a plus and minus deviation from the given dimension. Bilateral tolerances are preferred if deviation in either direction risks exceeding the given dimension and can be equal or unequal.

blade micrometer

A type of micrometer with flattened tips on the anvil and spindle. The blade micrometer is primarily used to measure the diameter of narrow grooves and slots.

blueprint

A document that contains all the instructions for a particular part and communicates all requirements necessary to manufacture and inspect a quality part. There are three main elements of a blueprint: the views, their dimensions, and the notes.

break lines

A wavy or irregular line. Break lines on a print define the boundary of an imaginary, broken-out section of a print or shorten dimensions that are very long.

burr

A rough edge on a metal part created as a result of cutting or machining. Burrs often need to be removed by grinding or creating a chamfer.

calculator

A small electronic device used to compute mathematical operations such as addition or subtraction, as well as more complex calculations. Calculators can reduce mathematical errors.

calculators

A small electronic device used to compute mathematical operations such as addition or subtraction, as well as more complex calculations. Calculators can reduce mathematical errors.

calipers

A measuring instrument with a pair of jaws on one end and a long beam containing a marked scale of unit divisions. The jaws can measure both internal and external features.

callouts

Information on a print that refers to a specific part feature rather than the whole part. Callouts, or local notes, communicate specifications such as chamfer angle and hole diameter.

celsius

°C. A unit of temperature measurement in the Metric System. One degree Celsius is equal to 33.8° Fahrenheit and 274.16° Kelvin.

center lines

A line made up of alternating long and short dashes. Center lines on a print define the center, or middle, of a symmetrical part.

center point

A single imaginary point located in the center and equally distant from the exterior of a circular feature. When a spherical surface forms a feature of size, it establishes the center point of that sphere.

centimeter

cm. A unit of length measurement in the metric system. One centimeter is equal to 0.394 inches.

chamfer

A small, angled surface added to an edge of a workpiece. A chamfer removes the sharp edge and helps eliminate burrs.

change block

The area of the blueprint indicating any changes or revisions made to the part views or dimensions. Change blocks should contain every revision, as well as the dates those revisions were made.

cross-section

The interior of a surface that is exposed when the part is cut. Cross-section views in prints provide clearer views of interior features, features with depth, and the workpiece material.

cutting-plane lines

A thick line, often dotted or dashed, with arrows at both ends. Cutting-plane lines on a print represent the path and position of an imaginary cut and are used with sectional views of parts.

datum reference frame

DRF. Three imaginary planes perpendicular to one another that are mapped onto the part. The datum reference frame provides an anchor for relating part features to each other.

decimal

A system of representing parts of a number using a period after a whole number. Decimal numbers grow increasingly smaller moving from left to right after the period.

depth

The top-to-bottom measurement of a hole, recess, or relief. Depth for a feature on a print is often specified in a callout.

depth micrometer

A type of micrometer with a spindle perpendicular to a flat base. The depth micrometer is primarily used to measure the depth of holes.

diameter

A line measuring the distance from one edge of a circle to the opposite edge that passes through the center. Diameter for various holes on a print are often specified in callouts.

dimension lines

A thick, solid line with arrows at both ends and a dimension in the center. Dimension lines on a print define the measurement of a part feature.

dimensions

The desired measurement of a feature on a part. A dimension is listed as a number given in the appropriate units.

engineers

A person responsible for designing parts, machines, and manufacturing operations. Engineers are responsible for drawing accurate and usable prints in metal cutting.

English system

A system of measurements based on the inch, pound, and degrees Fahrenheit primarily used in the United States and England. It is also known in the United States as the U.S. Customary System.

equations

A mathematical statement that shows the equality of two expressions. In 2 + 2 = 4, each side of the equation is a different way to express the same value.

extension lines

A thin, solid line that is perpendicular to a dimension line and placed at the end of a dimension line's arrow. Extension lines on a print connect the ends of a dimension line to the relevant part feature.

feature of size

FOS. A cylindrical surface, spherical surface, or two opposed parallel elements or surfaces that can be associated with a size dimension. A feature of size establishes an axis, median plane, or center point.

feature without size

A feature that cannot be associated with a size dimension. A single flat surface is a feature without size.

foot

ft. A unit of measurement used to measure length in the English system. One foot equals 30.48 centimeters.

fractions

A numerical expression with two numbers placed above and below a division line with the top number indicating how many parts of the bottom number are present in a measurement. Fractions can appear on their own or with a whole number.

geometric dimensioning and tolerancing

GD&T. An international standard for communicating instructions about the design and manufacturing of parts. GD&T uses universal symbols and emphasizes the function of the part.

graphing calculator

A digital calculator capable of plotting graphs, solving simultaneous equations, and performing tasks with variables. Graphing calculators can display several lines of text at once.

grid

The setup and structure of a print. Grids use letters and numbers positioned on the outer edges of a print to mark specific part locations.

groove micrometer

A type of micrometer with a long stem and two small discs at the end. The groove micrometer is primarily used to measure the width and position of internal grooves.

hidden lines

A thin line made up of a series of short dashes. Hidden lines on a print define part features that are not visible in that view of the part.

inch

in. A unit of measurement in the English system used to measure length. One inch equals approximately 2.54 centimeters.

informational blocks

A section of the print that contains background or general information about the print or part. Informational blocks include title and tolerance blocks.

International System of Units

SI. An internationally recognized standard system of measurements based on the meter, kilogram, and degrees Kelvin, among others. It is commonly called the metric system.

kelvin

°K. A unit of temperature measurement in the International System of Units. One degree Kelvin is equal to -457.87° Fahrenheit and -272.15° Celsius.

kilometer

km. A unit of length measurement in the metric system. One kilometer is equal to 0.621 miles.

leader lines

A thin line with an arrow pointing at a part feature. Leader lines on a print tie a dimension to a feature, especially when there is limited space on a print.

length

A measurement of distance from one point to another. Length is measured with inches and feet in English and meters in metric.

limit dimensions

A tolerancing method using an absolute maximum and minimum allowable dimension. Limit dimensions specify a range of acceptable measurements instead of target dimensions.

local notes

Information on a print that refers to a specific part feature rather than the whole part. Local notes, or callouts, communicate specifications such as chamfer angle and hole diameter.

mass

The amount of matter contained within an object. Mass gives an object weight when it is acted upon by gravity and is measured with Metric kilograms.

median plane

An imaginary, perfectly flat plane positioned in the middle between two opposing flat surfaces. These surfaces form a feature of size in GD&T, establishing the median plane between them.

memory

The place in an electronic device where data is held in storage. A basic calculator has four different memory functions.

meter

m. A unit of linear measurement in the metric system. One meter is equal to 3.281 feet.

metric system

An internationally recognized standard system of measurements based on the meter, kilogram, and degrees Celsius. It is also known as the International System of Units.

micrometer

A U-shaped measuring instrument with a threaded spindle that slowly advances toward a small anvil. Micrometers are available in numerous types for measuring assorted dimensions and features.

mile

mi. A unit of linear measurement in the English System that is used for long distances. A mile equals 1.609 kilometers.

millimeter

mm. A unit of length measurement in the metric system. One millimeter is equal to 0.039 inches.

object lines

A thick, solid line. Object lines, or visible lines, on a print represent edges of a part that can be seen from that particular view.

orthographic views

A print view that presents a series of illustrations that show a part's top and bottom, front and back, and right and left sides. Orthographic views communicate the shape and size of a part as well as clearly depict all its design elements.

perspectives

A specific point of view. Different perspectives show different sides and aspects of a part on a print.

print views

A representation of a part from a specific point of view created from a range of line types that illustrate a part's shape and design. Print views include orthographic, auxiliary, and section views.

scale

The relationship between the drawing of the part on the print and the actual finished part. Scale for an illustration will be given on a print, usually in the title block.

scientific calculator

A type of calculator used for calculating advanced scientific, mathematics, and engineering problems. Scientific calculators include trigonometric functions.

second

s. A unit of measurement used to describe time. There are 60 seconds in a minute, and 60 minutes in an hour.

section lines

Identifies the imaginary cut portion of a part in a section view. Section lines appear as a series of diagonal lines drawn close together.

section views

A print view that presents cross-section illustrations of a part that show its interior. A variety of section views may be contained in a print.

six degrees of freedom

The six basic possible linear and rotational movements that a part can have if left unrestricted. Positioning a part in the datum reference frame restricts all six degrees of freedom.

sloped

Rising or lowering at a gradual angle. Sloped surfaces on a part are easiest to see in an auxiliary print view.

spherical ball micrometer

A type of micrometer that is rounded for a precise measurement of any curved surface part. The spherical ball micrometer is more accurate than the standard flat pin micrometer and more durable than the point micrometer.

steel rule

A simple measuring instrument consisting of a long, thin metal strip with a marked scale of unit divisions. The steel rule comes in many sizes and forms and can be rigid or flexible.

stock

Raw material that is used to make manufactured parts. Stock is available in standard shapes such as long bars, plates, or sheets.

temperature

A measurement of the degree of the thermal energy in a substance. English units of temperature are degrees Fahrenheit, and metric units of temperature are degrees Celsius or Kelvin.

time

A measurement of the duration of an event from start to finish. Time is measured in seconds, minutes, and hours.

title blocks

A portion of a print that contains basic identifying information. Title blocks include information such as the company name, part name, part number, and engineer.

tolerance block

An informational block that details acceptable deviations from given dimensions for an entire part. Tolerance blocks are used when most part features have a similar tolerance range.

tolerances

An acceptable deviation from a specified part measurement. Tolerances usually include deviations that are larger or smaller than the intended design.

trigonometry

The branch of mathematics that addresses the measurements and relationships of a triangle and its parts. Scientific calculators are used to perform trigonometry.

unilateral tolerances

A tolerancing method using a deviation in only one direction, either plus or minus, from the specified dimension. Unilateral tolerances are used if variation in only one direction risks exceeding the given dimension.

vernier scale

A type of scale consisting of two opposing line markings with different divisions. Vernier scales appear on both manual and digital calipers and micrometers.

visible lines

A thick, solid line. Visible lines, or object lines, on a print represent edges of a part that can be seen from that particular view.

weight

A measurement of the gravitational pull on an object on the earth's surface. Weight is expressed in English pounds.

yard

yd. A unit of length measurement in the English system. One yard is equal to 0.914 meters.