Engineering Drawing - Part 3

Abbreviations of terms frequently used on drawings

Abbreviations are used on drawings to save time and space. Most of these conform to BS 8888. They are the same singular or plural, full stops are only used where word may be confusing.

A/C	Across corners
A/F	Across flats
HEX HD	Hexagon head
ASSY	Assembly
CRS	Centers
CL	Center line
CHAM	Chamfer
CH HD	Cheese head
CSK	Countersunk
CBORE	Counterbore
CYL	Cylinder or cylindrical
DIA	Diameter (in a note)
Ø	Diameter (preceding a dimension)
R	Radius (preceding a dimension, capital only)
RAD	Radius (in a note)
DRG	Drawing
FIG.	Figure
LH	Left hand
LG	Long
MATL	Material
NO.	Number
PATT NO.	Pattern number
PCD	Pitch circle diameter
I/D	Inside diameter
O/D	Outside diameter
RH	Right hand
RD HD	Round head
SCR	Screwed
SPEC	Specification
SPHERE	Spherical
SFACE	Spotface
SQ	Square (in a note)
TYP	Typical or typically
THK	Thick
□	Square (preceding a dimension)
STD	Standard
UCUT	Undercut
M/CD	Machined
mm	Millimeter
NTS	Not to scale
RPM	Revolutions per minute
SWG	Standard wire gauge
TPI	Teeth per inch

Sections

To show the inside details of a component it is imagined to be cut or sectioned along a plane, the cutting plane. Cutting planes are designated with capital letters, such as A-A in Figure 1 below. 

Figure 2

Figure 1

The side of the plane nearest the viewer is removed and the remaining details are shown as a sectional view, as demonstrated with section X-X in Figure 2. The arrows indicate the direction to view the component when defining the sectioned view. Note that First or Third angle orthographic projection systems are still used and are indicated by use of the appropriate symbols.

Sectional views are produced to:

• clarify details
• show internal features clearly
• reduce number of hidden detail lines required
• aid dimensioning
• show cross-section shape -->
• clarify an assembly

Surfaces cut by the cutting plane are usually hatched at an appropriate angle, say 45° with a density of lines in proportion with the component.

Symmetrical parts can be shown in half sections. Part or 'broken out' sections can be used.

Figure 4  Half section and a part or 'broken out' section.

Revolved sections are useful when clarifying local cross-section shapes as shown in Figure 5.

Figure 5

Figure 6  Web section

There are some exceptions to the general rules of sectioning:

• Webs, see Figure 6.
• Shafts, rods, spindles, see Figure 7.
• Bolts, nuts and thin washers.
• Rivets, dowels, pins and cotters.

These parts would not be shown as sections if their center lines lie on the cutting plane.

Figure 7

It may be appropriate to use Removed sections, for webs, beams or arms, as shown in Figure 8 below. Note the absence of viewing arrows.

Figure 8  Removed sections

Assemblies can be greatly clarified using sections. See the example as  shown below in Figure 9.

Note:

• Revolved sections.
• Part sections.
• Different hatching directions and spacings.
• Un-sectioned components such as shafts, keys, nuts etc.

Figure 9  An assembly drawing view, clarified using sections.