A Text Book on Engineering Graphics - Central Board of Secondary ...

(xiii) MAJOR DIAMETER OR OUTSIDE DIAMETER
MACHINE DRAWING
It is the diameter of an imaginary coaxial cylinder just touching the crest of
external threads or roots of internal threads. It is the largest diameter of a screw
thread.
(xiv) MINOR DIAMETER OR ROOT DIAMETER OR CORE DIAMETER
It is the diameter of an imaginary co-axial cylinder just touching the roots of
external threads or crest of internal threads.
(xv) NOMINAL DIAMETER
It is the diameter of the cylinder from which external threads are cut out. The
screw/bolt is specified by this diameter.
(xvi) FORM / PROFILE OF SCREW THREAD
P P
Fig 2.4
SECTION
PROFILE OF SCREW THREAD
The section of a thread cut by a plane containing the axis is known as the form of
the screw thread. It is also called the profile of the thread. Refer FIG 2.4
44 ENGINEERING GRAPHICS