ME 114 – Engineering Drawing II
SCREW THREADS, BOLTS and NUTS
Mechanical Engineering
University of Gaziantep
Dr. A. Tolga Bozdana
Assistant Professor
Threaded Fasteners
hThread is the helical grooves which are
opened to inner and outer surfaces. Fig. 1
shows the screw thread terminology.
hExternal thread (screw/vida - bolt/cıvata stud/saplama): A thread on the external
surface of a cylinder.
hInternal thread (nut/somun): A thread on the
internal surface of a cylinder.
hMajor diameter (diş üstü çap): The largest
diameter of a screw thread.
hMinor diameter (diş dibi çap): The smallest
diameter of a screw thread.
hPitch diameter (bölüm çapı): 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
1
Threaded Fasteners
h 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.
h 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.
h Depth of thread: The distance between crest and
root measured normal to the axis.
h Pitch (hatve, adım): The distance between
corresponding points on adjacent thread forms
measured parallel to the axis.
h Right-hand thread: A thread that when viewed
axially winds in a clockwise and receding direction.
Threads are RH unless otherwise specified.
h 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
2
Threaded Fasteners
h Lead: The distance a threaded part moves axially with respect to a fixed mating part,
in one complete revolution.
h 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).
h 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
3
Screw Thread Profiles
h Profiles of standard screw thread forms used in industry are shown in Fig. 3.
Figure 3
4
Screw Thread Representation
h External (Fig. 4) and internal (Fig. 5) screw threads are illustrated below.
h Thread notes are used in drawings in order to define type and size of screw threads.
British Type
.250-20 UNC-2A-LH
d e
a b c
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)
Metric Type
M20 x 2
x y z
x: Metric screw thread
y: Major diameter (mm)
z: Pitch (mm)
Figure 4
Figure 5
5
Threads for Specific Purposes
h Screw threads for blind holes with partially tapped
(Fig. 6) and bottom tapped (Fig. 7) are shown below.
h The chamfered view of screw threads is drawn only
for large chamfers (Fig. 8).
h There are also threaded parts on pipes for special
applications (Fig. 9).
Figure 8
Figure 6
Figure 9
Figure 7
6
Bolts, Nuts and Studs
h Fig. 10 shows a nut (unfaced and faced at bottom side)
and a bolt having hexagonal heads.
h There are five commonly used type of fasteners in
industry using bolts, nuts, cap screws and studs (Fig. 11).
h In most cases, the combination of bolt and nut, stud or
cap screw with hexagonal heads are used for holding
parts together.
Nut
Bolt
Figure 10
Figure 11
7
Assembly Drawings of Bolted and Stud Joints
R2
l
s
l0
R
r
H
A
K = 3d
l = tabulated
l0 = 2d to 2.5d
D
l2
l3
l1
l
m
h
A
A = 1.1d
s = 0.15d
c = s to 2s
R = 1.5d
r = based on R
R2 = 0.5c
n
l0
n
h = 0.7d
Dw = 2.2d
d1
m
c
D = 2d
H = 0.8d
R
r
s H
d1
d
d = major diameter
d1 = 0.85d
c
d
D
K
l2 = l1 + 0.5d
Dw
K
Dw
l1 = 1.25d
l3 = l1 + 0.4d
Figure 12
Bolted Joint
m = tabulated
n = tabulated
Figure 13
Stud Joint 8
Various Types of Bolts and Nuts
Figure 14
Figure 15
9