Page 271 - Aeronautical Engineer Data Book

Basic mechanical design 217
Table 12.2 Engineering abbreviations in common use:
Europe

Abbreviation Meaning
A/F Across flats
ASSY Assembly
CRS Centres
L or CL Centre line
CHAM Chamfered
CSK Countersunk
C’BORE Counterbore
CYL Cylinder or cylindrical
DIA Diameter (in a note)
Diameter (preceding a dimension)
DRG Drawing
EXT External
FIG. Figure
HEX Hexagon
INT Internal
LH Left hand
LG Long
MATL Material
MAX Maximum
MIN Minimum
NO. Number
PATT NO. Pattern number
PCD Pitch circle diameter
RAD Radius (in a note)
R Radius (preceding a dimension)
REQD Required
RH Right hand
SCR Screwed
SH Sheet
SK Sketch
SPEC Specification
SQ Square (in a note)
Square (preceding a dimension)
STD Standard
VOL Volume
WT Weight

12.3 Datums and tolerances – principles
A datum is a reference point or surface from
which all other dimensions of a component are
taken; these other dimensions are said to be
referred to the datum. In most practical designs,
a datum surface is normally used, this generally
being one of the surfaces of the machine element