ALIGNED SECTION—A section view in which some internal features are revolved into or out of the
plane of the view.
ANALOG—The processing of data by continuously variable values.
ANGLE—A figure formed by two lines or planes extending from, or diverging at, the same point.
APEX—The highest point or peak.
APPLICATION BLOCK—A part of a drawing of a subassembly showing the reference number for the
drawing of the assembly or adjacent subassembly.
ARC—A portion of the circumference of a circle.
ARCHITECT’S SCALE—Scale used when dimensions or measurements need to be expressed in
feet and inches.
AUXILIARY VIEW—An additional plane of an object, drawn as if viewed from a different location. It is
used to show features not visible in the normal projections.
AXIS—The center line running lengthwise through a screw.
AXONOMETRIC PROJECTION—A set of three or more views in which the object appears to be
rotated at an angle, so that more than one side is seen.
BAR JOISTS—Light steel joists of open-web construction with a single zigzag bar welded to upper
and lower chords at the points of contact. Bar joists are used as floor and roof supports.
BATTER BOARDS—Pairs of horizontal boards nailed to wood stakes adjoining an excavation. Used
with strings as a guide to elevation and to outline a proposed building.
BEAM—Any horizontal load-bearing structural member that spans a space and is supported at both
ends.
BEARING CAPACITY—The maximum unit pressure that soil or other material can withstand without
failure or excessive settlement.
BENCH MARK—A mark made by a surveyor or contractor that is used as a reference point when
measuring the elevation or location of other points.
BEND ALLOWANCE—An additional amount of metal used in a bend in metal fabrication.

BILL OF MATERIAL—A list of standard parts or raw materials needed to fabricate an item.
BISECT—To divide into two equal parts.
BLOCK DIAGRAM—A diagram in which the major components of a piece of equipment or a system
are represented by squares, rectangles, or other geometric figures, and the normal order of progression of a signal or current flow is represented by lines.
BLUEPRINTS—Copies of mechanical or other types of technical drawings. Although blueprints used
to be blue, modern reproduction techniques now permit printing of black-on-white as well as colors.
BORDER LINES—Dark lines defining the inside edge of the margin on a drawing.
BREAK LINES—Lines to reduce the graphic size of an object, generally to conserve paper space.
There are two types: the long, thin, ruled line with freehand zigzag and the short, thick, wavy freehand
line.
BROKEN-OUT SECTION—Similar to a half section; used when a partial view of an internal feature is
sufficient.
CANTILEVER—A horizontal structural member supported only by one end.
CAST—A metal object made by pouring melted metal into a mold.
CENTER LINES—Lines that indicate the center of a circle, arc, or any symmetrical object; consist of
alternate long and short dashes evenly spaced.
CHORDS—The basic components of a roof truss are the top and bottom chords and the web
members. The top chords serve as roof rafters. The bottom chords act as ceiling joists.
CIRCLE—A closed plane figure having every point on its circumference (perimeter) equidistant from
its center.
CIRCUMFERENCE—The length of a line that forms a circle.
CLEVIS—An open-throated fitting for the end of a rod or shaft, having the ends drilled for a bolt or a
pin. It provides a hinging effect for flexibility in one plane.
COLUMN—High-strength vertical structural members.
COMPUTER LOGIC—The electrical decision process used by a computer to perform calculations
and other functions.
COMPUTER NUMERICAL CONTROL—A process in which a machine is controlled by the input
media from a computer to produce machined parts.
COMPUTER-AIDED DRAFTING (CAD)—A process in which engineering drawings are developed
using a computer.
COMPUTER-AIDED MANUFACTURING (CAM)—A method by which a computer uses a design to
guide a machine that produces parts.
CONE—A solid figure that tapers uniformly from a circular base to a point.
CONSTRUCTION LINES—Lightly drawn lines used in the preliminary layout of a drawing.
CORNER POSTS—Vertical members located at the corners of a timber structure.
CORNICE—The projecting or overhanging structural section of a roof.
CREST—The surface of the thread corresponding to the major diameter of an external thread and the
minor diameter of an internal thread.
CUBE—Rectangular solid figure in which all six faces are square.

CUTTING PLANE LINE—A line indicating a plane or planes from which a sectional view is taken.
CYLINDER—A solid figure with two equal circular bases.
DEAD LOAD—A calculation of the weight of a building’s structural components, fixtures, and
permanently attached equipment, used in designing a building and its foundations.
DEPTH—The distance from the root of a thread to the crest, measured perpendicularly to the axis.
DEVELOPMENT—The process of making a pattern from the dimensions of a drawing, used in
fabricating sheet metal objects.
DIGITAL—The processing of data by numerical or discrete units.
DIMENSION LINE—A thin broken line (except in the case of structural drafting) with each end
terminating with an arrowhead; used to define the dimensions of an object.
DRAWING NUMBER—An identifying number assigned to a drawing or a series of drawings.
DRAWINGS—The original graphic design from which a blueprint may be made; also called plans.
ELECTROMECHANICAL DRAWING—A special type of drawing combining electrical symbols and
mechanical drawing to show the position of equipment that combines electrical and mechanical
features.
ELEMENTARY WIRING DIAGRAM—A wiring diagram that shows the electrical connections and
functions of a specific circuit arrangement. Elementary wiring diagram is sometimes used
interchangeably with schematic diagram, especially for a simplified schematic diagram.
ELEVATION—A drawing showing the front, rear, and sides of a structure, as they would appear
projected on vertical planes.
EXPLODED VIEW—A special view of a device that shows the relative location of part. An exploded
view can be particularly helpful in assembling complex objects.
EXTERNAL THREAD—A thread on the outside of a member. For example, the thread of a bolt.
FALSEWORK—Temporary supports of timber or steel sometimes required in the erection of difficult
or important structures.
FILLET—A concave internal corner of a metal component.
FINISH MARKS—Marks used to indicate the degree of finish to be achieved on surfaces to be
machined.
FOOTINGS—Weight-bearing elements at the lower end of a wall used to distribute a load to a wider
area of supporting soil.
FORMAT—The general makeup or style of a drawing.
FRENCH CURVE—An instrument used to draw smooth irregular curves.
FRUSTUM—A truncated cone or pyramid in which the plane cutting off the apex is parallel to the
base.
FULL SECTION—A sectional view that passes entirely through the object.
GIRDER—A large principal beam of steel, reinforced concrete, wood, or a combination of these, used
to support other structural members at isolated points along its length.
GUSSET PLATES—A plate fastened across a joint for reinforcement in wood or steel framework
members.

HALF SECTION—A combination of an orthographic projection and a section view to show two halves
of a symmetrical object.
HATCHING—Lines that are drawn on the internal surface of sectional views. Hatching is used to
define the kind or type of material the section surface consists of.
HELIX—The curve formed on any cylinder by a straight line in a plane that is wrapped around the
cylinder with a forward progression.
HIDDEN LINES—Medium, short, dashed lines that indicate the hidden features of the object being
drawn.
INTERCONNECTION DIAGRAM—Used to show the cabling between electronic units and to indicate
the terminal connections.
INTERNAL THREAD—A thread on the inside of a member. For example, the thread inside a nut.
ISOMETRIC DRAWING—A type of pictorial drawing. See ISOMETRIC PROJECTION.
ISOMETRIC PROJECTION—A form of graphical projection, or more specifically, a form of
axonometric projection; a method of visually representing three-dimensional objects in two
dimensions, in which the three coordinate axes appear equally foreshortened and the angles between
any two of them are 120 degrees.
ISOMETRIC WIRING DIAGRAM—A diagram showing the outline of a ship, an aircraft, or other
structure, and the location of equipment such as panels and connection boxes and cable runs.
JOIST—A horizontal supporting member that runs from wall to wall, wall to beam, or beam to beam
to support a ceiling, roof, or floor.
KEY—A small wedge or rectangular piece of metal inserted in a slot or groove between a shaft and a
hub to prevent slippage.
KEYSEAT—A slot or groove into which the key fits.
KEYWAY—A slot or groove within a cylindrical tube or pipe into which a key fitted into a key seat will
slide.
LEAD—The distance a screw thread advances in one turn, measured parallel to the axis. On a
single-thread screw the lead and the pitch are identical; on a double-thread screw the lead is twice
the pitch; on a triple-thread screw the lead is three times the pitch.
LEADER LINES—Thin lines used to connect numbers, references, or notes to appropriate surfaces
or lines.
LEGEND—A description of any special or unusual marks, symbols, or line connections used in the
drawing.
LINTEL—A horizontal beam used in the construction of buildings. It usually supports the masonry
above a window or door opening, and is also known as a header.
LOGIC DIAGRAM—A type of schematic diagram using special symbols to show components that
perform a logic or information processing function.
MAJOR DIAMETER—The largest diameter of an internal or external thread.
MILITARY STANDARD (MIL-STD)—A formalized set of standards for supplies, equipment, and
design work purchased by the United States Armed Forces.
MINOR DIAMETER—The smallest diameter of an internal or external thread.
NOTES—Descriptive writing on a drawing to give verbal instructions or additional information.

OBLIQUE PROJECTION—A view produced when the projectors are at an angle to the plane of the
object illustrated. Vertical lines in the view may not have the same scale as horizontal lines.
OFFSET SECTION—A section view of two or more planes in an object to show features that do not
lie in the same plane.
ONBOARD PLANS—See SHIP’S PLANS.
ORTHOGRAPHIC PROJECTION—A means of representing a three-dimensional object in two
dimensions; with multiview orthographic projections, up to six pictures of an object are produced, with
each projection plane parallel to one of the coordinate axes of the object.
PARTIAL SECTION—A sectional view consisting of less than a half section, which is used to show
the internal structure of a small portion of an object, also known as a broken section.
PERPENDICULAR—The line or view from an object at 90 degrees.
PERSPECTIVE—The visual impression that, as parallel lines project to a greater distance, the lines
move closer together.
PHANTOM LINES—Lines showing the alternate position of a movable object.
PHASE—An impulse of alternating current. The number of phases is dependent on the generator
windings. Most large generators produce a three-phase current that must be carried on at least three
wires.
PICTORIAL DRAWING—A drawing that gives the real appearance of the object, showing general
location, function, and appearance of parts and assemblies.
PICTORIAL WIRING DIAGRAM—A diagram showing various parts of a piece of equipment or
system and the electrical wiring between the parts.
PIER—A vertical support for a building or structure, usually designed to hold substantial loads.
PILASTERS—Columns built within a wall, usually projecting beyond the wall.
PILLAR—A high-strength vertical structural member.
PITCH—The distance from a point on a screw thread to a corresponding point on the next thread,
measured parallel to the axis.
PLAN VIEW—A view of an object or area as it would appear from directly above.
PLANE—A longitudinal section through the axis of an object.
PLOT PLAN—A map or plan view of a lot showing the survey marks, including the bench mark (BM),
with the elevations and the grading requirements.
POLARITY—The direction of magnetism or direction of flow of current.
PROJECTION—A technique for showing one or more sides of an object to give the impression of a
drawing of a solid object.
PROJECTOR—The theoretical extended line of sight used to create a perspective view or pictorial
drawing of an object.
RADIUS—A straight line from the center of a circle or sphere to its circumference or surface.
RAFTER—The horizontal or inclined members that provide support to a roof.
RAFTER PLATES—Horizontal members that support the wall ends of rafters.
REFERENCE DESIGNATION—A combination of letters and numbers to identify parts on electrical
and electronic drawings, diagrams, parts lists.

REFERENCE NUMBERS—Numbers used on a drawing to refer the reader to another drawing for
more detail or other information.
REMOVED SECTION—A special view to illustrate a particular cross section of an object.
REVISION BLOCK—This block is located in the upper right corner of a print. It provides a space to
record any changes made to the original print.
REVOLVED SECTION—A drawing of an object’s internal cross section superimposed on the basic
drawing of the object.
RIDGE—The lengthwise member at a right angle to the rafters, which supports the peak ends of the
rafters in a roof.
RIDGEBOARD—The longitudinal board, set on edge, used to support the upper ends of the rafters,
also known as a ridgepole.
ROOT—The area at the bottom of the thread. This area of the thread corresponds to the minor
diameter of an external thread and the major diameter of an internal thread.
ROUND—The outside corners of a metal object that have been rounded to prevent chipping and to
avoid sharp edges.
SCALE—The relationship between the measurement used on a drawing and the measurement of the
actual object. Also a measuring device, such as a ruler, having special graduations.
SCHEMATIC DIAGRAM—A picture of a circuit that uses symbols to represent the components in the
circuit.
SECTION—A view showing a clearer view of interior or hidden features of an object that cannot be
observed in conventional outside views.
SECTION LINES—Thick solid lines with an arrowhead used to indicate the direction in which a
section or plane is viewed or taken.
SECTIONAL VIEWS—Provide important information about the height, materials, fastening and
support systems, and concealed features of a structure.
SHIP’S PLANS—A set of drawings that show all of the significant construction features and
equipment needed to operate and maintain a ship, also known as onboard plans.
SILL—A horizontal structural member that supports the ends of floor beams or joists in wood frame
construction.
SINGLE-LINE DIAGRAM—A diagram using single lines and graphic symbols to show all
components in a circuit or system.
SITE PLAN—Shows the contours, boundaries, roads, utilities, trees, structures, and any other
significant physical features on or near the construction site.
SOLEPLATE—A horizontal structural member used as a base for studs or columns.
SPECIFICATION—A detailed description or identification describing items so they can be
manufactured, assembled, and maintained according to their performance requirements.
SPREAD FOOTINGS—Generally rectangular prisms of concrete, larger in lateral dimensions than
the column or wall they support; used to distribute the load of a column or wall to the subgrade.
STATION NUMBERS—Designations of reference lines used to indicate linear positions along a
component such as an airframe or a ship’s hull.
STEEL PLATE—Flat steel that has a width of greater than 8 inches and a thickness of 1/4 inch or
greater.

STUD—The chief vertical structural members in light frame construction, used as part of a wall and
for supporting moderate loads.
SUPERSTRUCTURE—The part of a bridge above the beam seats or the spring line of an arch.
SYMBOL—A graphical representation of the component or part shown in a drawing.
TEMPLATE—A piece of thin material used as a true-scale guide or as a model for reproducing
various shapes.
TITLE BLOCK—A blocked area in the lower right corner of the print. Provides information to identify
the drawing number, name of the part or assembly that it represents, and all information required to
identify the part or assembly.
TOLERANCE—The amount that a manufactured part may vary from its specified size.
TOP PLATE—A horizontal member at the top of an outer building wall; used to support a rafter.
TOTAL DEAD LOAD—The total weight of the structure, which gradually increases as the structure
rises and remains constant once it is complete.
TOTAL LIVE LOAD—The total weight of movable objects, such as people, furniture, and bridge
traffic, the structure happens to be supporting at a particular instant.
TRACING PAPER—High-grade, white, translucent paper that takes pencil well; can be used to make
reproductions of drawings.
TRIANGULATION—A technique for making developments of complex sheet metal forms using
geometrical constructions to translate dimensions from the drawing to the pattern.
TRUSS—A beam of given strength without intermediate supports. A truss can support a given load
over a specific maximum span.
TRUSS—A combination of members, such as beams, bars, and ties, usually arranged in triangular
units, that forms a rigid framework for supporting loads over a span.
UTILITY PLAN—A floor plan that shows the layout of heating, electrical, plumbing, or other utility
systems.
VERTEX—A corner or a point where lines meet.
VIEW—A drawing of a side or plane of an object as seen from one point.
WIRING (CONNECTION) DIAGRAM—A detailed diagram of each circuit installation showing all of
the wiring, connectors, terminal boards, and electrical or electronic components of the circuit.
ZONE NUMBERS—Numbers and letters printed on the borders of maps used to locate a particular
point or part on the map.