Abbreviations and Their Uses (Leaving Cert DCG): Revision Notes
Abbreviations and Their Uses
Technical drawings contain numerous abbreviations that help save space while maintaining clarity and precision. Understanding these abbreviations is essential for interpreting assembly drawings and engineering specifications correctly. These standardised shortcuts allow engineers and designers to communicate complex information efficiently without cluttering drawings with lengthy explanations.
Why abbreviations matter in technical drawing
Abbreviations serve several important purposes in technical drawing. They help keep drawings clean and readable by reducing text clutter, ensure consistency across different drawings and designers, save valuable space on detailed technical drawings, and follow international standards that make drawings universally understood by professionals.
When creating assembly drawings, you'll encounter abbreviations for measurements, fastener types, drawing conventions, and specifications. Learning these abbreviations will help you read and create professional technical drawings more effectively.
Measurement and dimensional abbreviations
These abbreviations relate to how dimensions and measurements are specified on technical drawings.
A/C stands for "Across corners" and refers to measuring the distance across the corners of a hexagonal shape. This is particularly important when specifying hex nuts or bolt heads where you need to know the diagonal measurement.
A/F means "Across flats" and indicates the measurement across the flat sides of a hexagonal shape. This is the most common way to specify spanners or socket sizes for hex nuts and bolts.
DIA represents diameter and is often used in notes and specifications. The symbol Ø (diameter symbol) is placed before a dimension to indicate diameter measurement in the actual drawing.
R indicates radius and should always be written as a capital letter. It precedes radius dimensions on technical drawings.
PCD stands for "Pitch circle diameter" - this is the diameter of the circle on which bolt holes are positioned in circular patterns, commonly used for flanged connections. This is crucial for ensuring proper bolt alignment in circular assemblies.
Fastener abbreviations
Fasteners are critical components in assemblies, and various abbreviations describe different screw and bolt head types.
CH HD refers to "Cheese head" screws or bolts, which have a cylindrical head with a flat top, resembling a wheel of cheese.
CSK stands for "Countersunk head screw" - these screws have angled heads designed to sit flush with or below the surface of the material.
RD HD means "Round head" and describes screws with dome-shaped heads that sit above the surface.
HEX HD indicates "Hexagonal head" fasteners, which require hex keys or spanners for installation.
SCR simply means "Screwed" and indicates threaded connections or fasteners.
Practical Application: Choosing the Right Fastener
When designing an assembly where the screw head must not protrude above the surface, you would specify CSK (countersunk) screws. For applications where easy removal is important, HEX HD (hexagonal head) fasteners provide better grip for tools.
Drawing convention abbreviations
These abbreviations describe standard drawing practices and construction details.
CL represents "Centre line" - these are the dashed lines that show the central axis of symmetrical objects or indicate the centre of holes and circular features.
CHAM stands for "Chamfered" and indicates that an edge has been cut at an angle, typically 45 degrees, to remove sharp corners.
C'BORE refers to "Counterbore" - a larger diameter hole that's drilled partway through material to allow bolt heads or nuts to sit below the surface.
U/CUT means "Undercut" and describes a groove or recess cut into material, often used to ensure proper fit between components.
Centre lines (CL) are fundamental to technical drawing as they help establish symmetry and provide reference points for dimensioning. Always ensure centre lines extend slightly beyond the outline of the object they represent.
Assembly and construction abbreviations
These terms relate to how components fit together and are manufactured.
ASSY is short for "Assembly" and refers to a collection of parts that work together as a unit.
CRS stands for "Centres" and indicates the distance between the centres of holes, shafts, or other features.
CYL means "Cylindrical" and describes round, tube-like shapes.
Material and specification abbreviations
These abbreviations help specify materials, standards, and requirements.
MATL represents "Material" and is used in notes describing what material a component should be made from.
SPEC stands for "Specification" and refers to detailed technical requirements or standards that must be met.
STD means "Standard" and indicates that a component should conform to established industrial standards.
INSUL refers to "Insulated or insulation" and describes components that prevent electrical or thermal conduction.
Always verify that STD (standard) components meet the specific requirements of your application. Different industries may use different standards for similar components.
Directional and positional abbreviations
These terms help specify orientation and positioning of components.
LH means "Left hand" and RH means "Right hand" - these are particularly important for threaded components, as threads can be cut in either direction.
INT stands for "Internal" (inside) and EXT means "External" (outside) - these help specify whether features like threads are on the inside or outside of components.
LG simply means "Long" and helps distinguish between different lengths of similar components.
Thread Direction Example
A RH (right hand) thread tightens when turned clockwise, while a LH (left hand) thread tightens when turned counter-clockwise. Left hand threads are often used in rotating machinery to prevent components from loosening due to rotation.
Drawing status and miscellaneous abbreviations
These abbreviations provide information about the drawing itself or measurement specifications.
SK stands for "Sketch" and indicates a preliminary or rough drawing.
SH means "Sheet" and refers to individual pages in a set of drawings.
REQD is short for "Required" and indicates mandatory specifications or quantities.
NTS means "Not to scale" and warns that dimensions cannot be measured directly from the drawing.
RPM stands for "Revolutions per minute" and describes rotational speed.
FIM means "Full indicated movement" and relates to measurement precision in engineering applications.
MAX and MIN represent "Maximum and minimum" values for dimensional tolerances.
No. is simply "Number" and precedes numerical identifiers.
SQ indicates "Square" when used in notes, and the square symbol □ precedes square dimensions.
FIG stands for "Figure" and DRG means "Drawing" - these help reference illustrations and technical drawings.
Always check if a drawing is marked NTS (Not to Scale) before attempting to take measurements directly from the drawing. Rely on the stated dimensions instead.
Key Points to Remember:
- Abbreviations save space and maintain drawing clarity - learn the common ones to read technical drawings effectively
- Fastener abbreviations (CH HD, CSK, RD HD) help specify the correct screw types for assemblies
- Measurement abbreviations (A/C, A/F, DIA, R) are essential for understanding dimensions and tolerances
- Drawing convention abbreviations (CL, CHAM, C'BORE) describe standard construction details and features
- Always check if a drawing is NTS (Not to Scale) before taking measurements directly from the drawing
- Thread direction (LH vs RH) is critical for proper assembly of threaded components