Alphabet of Lines
Used to represent visible edges and outlines of the object being drawn
Visible Line
BC
Bolt Circle
Hot Rolled Steel
HRS
MIN
Minimum/Minute
SECT
Section
Indicates symmetry, center points, or axes. Consists of alternate long and short dashes.
CI
Cast Iron
GRD
Grind
Not to Scale
NTS
Typical
TYP
Represents edges and outlines of an object that are not visible in the given view.
Hidden Line
Chamfer
CHAM
Gage
GA
Ream
RM
SCR
Screw
Appear only on a sectional view where the surface has been cut. Normally drawn diagonally.
Section Lines
Counterbore
CBORE
ID
Inside Diameter
REF
Reference
THD
Thread
Terminates a view to conserve space and avoid congestion. Also separates internal and external features with broken-out sections.
Short Break Line
CSK
Countersink
HT TR
Heat Treat
MI
Malleable Iron
Tolerance
TOL