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ME 114 Engineering Drawing II
Dr. Ouzhan YILMAZ Associate Professor
Mechanical Engineering
University of Gaziantep
SCREW THREADS, BOLTS and NUTS
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1
Threaded Fasteners
Thread is the helical grooves which are opened to
inner and outer surfaces. Fig. 1 shows the screw
thread terminology.
External thread (screw): A thread on the external
surface of a cylinder.
Internal thread (nut): A thread on the internal
surface of a cylinder.
Major diameter (di st ap): The largest
diameter of a screw thread.
Minor diameter (di dibi ap): The smallest
diameter of a screw thread.
Pitch diameter (blm ap): The diameter of an
imaginary cylinder, the surface of which cuts the
thread forms where the width of the thread and
groove are equal.
Figure 1
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2
Threaded Fasteners
Crest: The edge or surface that joins the sides of a
thread and is farthest from the cylinder or cone
from which the thread projects.
Root: The edge or surface that joins the sides of
adjacent thread forms and coincides with the
cylinder or cone from which the thread projects.
Depth of threat: The distance between crest and
root measured normal to the axis.
Pitch (hatve, adm): The distance between
corresponding points on adjacent thread forms
measured parallel to the axis.
Right-hand thread: A thread that when viewed
axially winds in a clockwise and receding
direction. Threads are RH unless otherwise
specified.
Left-hand thread: A thread that when viewed
axially winds in a counterclockwise and receding
direction. All left-hand threads are designated LH. Figure 1
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3
Threaded Fasteners
Lead: The distance a threaded part moves axially with respect to
a fixed mating part,
in one complete revolution.
Single thread: A thread having the thread form produced on only
one helix of cylinder.
On a single thread, the lead and pitch are equivalent. Threads
are always single
unless otherwise specified (Fig. 2).
Multiple thread: A thread combination having the same form
produced on two or
more helices. For a multiple thread, the lead is an integral
multiple of the pitch (e.g.
on a double thread, lead is twice the pitch). A multiple thread
permits a more rapid
advance without a coarser (larger) thread form (Fig. 2).
Figure 2
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4
Screw Thread Profiles
Figure 3
Profiles of standard screw thread forms used in industry are
shown in Fig. 3.
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5
Screw Thread Representation
External (Fig. 4) and internal (Fig. 5) screw threads are
illustrated below.
Thread notes are used in drawings in order to define type and
size of screw threads.
.250-20 UNC-2A-LH
a b c d e
a: Major diameter (inch)
b: Threads per inch
c: Form (i.e. Unified National Coarse)
d: External thread (B for internal)
e: Left-hand thread (RH for right-hand)
British Type Metric Type
M20 x 2
x y z
x: Metric screw thread
y: Major diameter (mm)
z: Pitch (mm)
Figure 5
Figure 4
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6
Threads for Specific Purposes
Screw threads for blind holes with partially tapped
(Fig. 6) and bottom tapped (Fig. 7) are shown below.
The chamfered view of screw threads is drawn only
for large chamfers (Fig. 8).
There are also threaded parts on pipes for special
applications (Fig. 9).
Figure 7
Figure 6
Figure 8
Figure 9
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7
Bolts, Nuts and Studs
Fig. 10 shows a nut (unfaced and faced at bottom side)
and a bolt having hexagonal heads.
There are five commonly used type of fasteners in
industry using bolts, nuts, cap screws and studs (Fig. 11).
In most cases, the combination of bolt and nut, stud or
cap screw with hexagonal heads are used for holding
parts together.
Figure 11
Nut Bolt
Figure 10
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8
Assembly Drawings of Bolted and Stud Joints
tabulated
tabulated
4.0
5.0
25.1
5.2 to2
tabulated
3
5.0
on based
5.1
2 to
15.0
1.1
2.2
7.0
8.0
2
85.0
diametermajor
3
12
1
0
2
1
n
m
dll
dll
dl
ddl
l
dK
cR
Rr
dR
ssc
ds
dA
dD
dh
dH
dD
dd
d
w
Figure 12 Bolted Joint Figure 13 Stud Joint
d 1
d
c
H
s n
m
h
D
A
l 0
l K
D w
d 1
d
H
s
n
m
l 0
l K
D w
A
l 1
l 2 l 3
D
c
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9
Various Types of Bolts and Nuts
Figure 14
Figure 15
