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

MACHINE DRAWING
2.5 BOLTS
In day to day life, we can observe many machine parts joined by bolt and nut. Now, let us study
about the bolts.
A bolt consists of a cylindrical body with one end threaded and the other end converted into a
head. It is passed through clearance holes (diameter slightly more than nominal diameter of bolt)
in two or more aligned parts. A nut is screwed on the threaded end of the bolt to tighten the parts
together. Different types of bolts are used for different purposes. The shape of the head also
depends upon the purpose for which the bolt is used. The length of a bolt is its total length,
"excluding the height or thickness of bolt head". Bolt has external thread. An external thread is
represented by "discontinuous, minor diameter circle".
Fig 2.11a
We are going to study about the following types of bolts
(i) Hexagonal headed bolt
(ii) Square headed bolt
(iii) Tee headed bolt
(iv) Hook bolt
2.5.1 HEXAGONAL HEADED BOLT
THREADED LENGTH
T LENGTH OF THE BOLT
THICKNESS OF
THE BOLT HEAD
SQUARE BOLT
It is the most commonly used form of the bolt. The head of a
hexagonal head bolt is a hexagonal prism with a conical
chamfer rounded off at an angle of 30° on the outer end face.
All dimensions of a hexagonal head bolt and hexagonal nut are
same except the height or thickness of the hexagonal head. The
approximate height/thickness of the bolt head is 0.8d (d is the
diameter of the bolt). A little portion (about 3 mm) of the
threaded end should remain outside the nut.
Let us now learn to draw the views of a hexagonal headed bolt.
ENGINEERING GRAPHICS 51