Screw Thread Terms for beginners in engineering- Gdlc(1).pdf

Screw thread terminologies for beginners

1. 51

Screw Threads
Nuts and Bolts
UNIT 3 SCREW THREADS, NUTS AND BOLTS
Structure
3.1 Introduction
Objectives
3.2 Screw Thread Terms
3.3 Standard Thread Forms
3.4 Right and Left Hand Threads
3.5 Single and Multiple Start Threads
3.6 Thread Profile Types
3.6.1 Sharp V - Thread
3.6.2 Whitworth Standard Thread
3.6.3 British Association Thread
3.6.4 American National Thread
3.6.5 Unified Standard Thread
3.7 Square, Acme and Buttress Threads
3.8 Representation of Threads
3.9 Nut and Bolt
3.10 Shape of Bolt Head and Nut
3.11 Procedure of Drawing
3.12 Drawing Complete Bolt
3.13 Square Headed Bolt and Square Nut
3.14 Washer
3.15 Stud
3.16 Eye Bolt
3.17 Other Bolt Heads
3.18 Other Nut Shapes
3.19 Summary
3.20 Answers to SAQs

3.1 INTRODUCTION
Machines are assembled from individual parts. The parts may need to be joined
sometimes in permanent or temporary connections. The temporary connections or joints
are normally made by using screws bolts or nuts and bolts. The temporary joints render
the convenience of disconnection as frequently as required for such purposes as
inspection, repairs, adjustment or replacement. The most important feature of the screws
or bolt is that they are standardized and are available as standard part ready to use.
The threaded fasteners are used to hold two parts. The fastener consists of two parts. An
externally threaded member whose length is normally greater than the diameter carries
threads over entire or part length from end. The other end of this member is larger in area
(you can assume that the end is upset). This part is inserted in coaxial holes in two parts
taking care that the “upset” or larger end is greater in dimension than the holes so that it
does not pass through the hole. The end that comes out of the holes carries thread upon
which another internally threaded part is wound.

2. 52
Machine Drawing In this unit we will study the geometrical characteristics of threads, forms of threads and
profiles, their standards and geometrical proportions, nuts and bolts, washer, stud and
methods of drawing.
Objectives
After studying this unit you should be able to learn
• terminology of threads,
• standard thread profiles and other profiles,
• geometrical proportions of thread,
• how to draw thread,
• what is a bolt and a nut,
• what shapes the bolt head and nut have,
• how to draw the bolts and nuts,
• what are the types of bolt heads and nuts, and
• how are the bolted joints made and how are they drawn.
3.2 SCREW THREAD TERMS
Figure 3.1 shows a V-thread and a square thread. The various terms associated with
threads are introduced and defined. The figures may be referred to for clear
understanding.
Thread
By cutting a helical groove on a cylindrical surface what is left is called thread.
Carefully the cross section of the groove is maintained uniform so that the
cross-section of the thread left on the cylindrical surface is also uniform. The
threads can be made (or cut) both on external cylindrical surface or internal
cylindrical surface to obtain respectively the external threads or internal threads.

(a) V-Thread (External) (b) Square Thread (External) (c) Internal Thread
Figure 3.1
Flank
The thread profile is made up of two straight sides called flank. The flanks of the
same profile of V-thread join at the top surface called crest. The adjacent flanks
on two thread profiles join at the root.
Thread Angle
This is the angle included between flanks of a thread profile.
Pitch
The axial distance measured between corresponding points on adjacent threads is
known as pitch while the distance through which the screw advances axially in
one rotation is called lead.

3. 53

Screw Threads
Nuts and Bolts Diameters
The diameter of an imaginary cylinder whose internal surface is tangential to the
crest is called the major diameter (d). The diameter of an imaginary cylinder
touching the roots of the thread is known as minor diameter. The diameter of the
imaginary surface that passes between the crest and root and cuts the thread
profile such that the width of the thread is equal to the width of the space, is
called the mean diameter.
Pitch Line and Thread Thickness
The pitch line can be regarded as the generator of the pitch surface and the
thickness of the thread measured along the pitch line is known as thread
thickness.
3.3 STANDARD THREAD FORMS
The basic profile of ISO metric screw thread is shown in Figure 3.2. BIS (Bureau of
Indian Standard) has adopted the same thread form as in the practice in several other
countries.

Figure 3.2 : ISO Metric Screw Thread
The thread is characterized by angle of 60
o
between the flanks and pitch, denoted by p.
The theoretical depth, H is related to p as
H = 0.866025 p
Certain practical changes are introduced in manufactured threads according to design
profiles of threads. Figure 3.3 shows design profile for external and internal threads. The
various diameters are denoted as under:
External Threads
Major diameter – d
Minor diameter – d
1 or d 3 or d c
Pitch diameter – d
2 or d m or d p
Internal Threads
Major diameter – D
Minor diameter – D
1
Pitch diameter – D
2
Other dimensions are shown in Figure 3.2 and 3.3.

4. 54
Machine Drawing Practical design form of thread avoids sharp corners. They are changed to flat tips and
radiused grooves.

Figure 3.3 : Practical Design Form of Thread
The BIS 1362 – 1962 designates threads by M followed by major (nominal) diameter.
M 2.5 means a screw or bolt of major diameter of 2.5 mm. Tables 3.1 and 3.2
respectively describe dimensions of V-threads coarse and V-threads fine. While the
coarse thread carries only one number (for major diameter) the fine thread is designated
by two numbers for major diameter and pitch.
Table 3.1
d
c
(mm)
Designation P (mm)
D or,
D (mm)
d
p
(mm)
Nut Bolt
Thread Depth
(mm)
M 0.4 0.1 0.400 0.335 0.292 0.277 0.61
M 0.8 0.2 0.800 0.670 0.584 0.555 0.123
M1 0.25 1.000 0.838 0.729 0.693 0.153
M 1.4 0.3 1.400 1.205 01.075 1.032 0.184
M 1.8 0.35 1.800 1.573 1.421 1.371 0.215
M 2 0.4 2.000 1.740 1.567 1.509 0.245
M 2.5 0.45 2.500 2.208 2.013 1.948 0.276
M 3 0.5 3.000 2.675 2.459 2.387 0.307
M 3.5 0.6 0.500 3.110 2.850 2.764 0.368
M 4 0.7 4.000 3.545 3.242 3.141 0.429
M 5 0.8 5.000 4.480 4.134 4.019 0.491
M 6 1 6.000 5.350 4.918 4.773 0.613
M 8 1.25 8.000 7.188 6.647 6.466 0.767
M 10 1.5 10.000 9.026 8.876 8.160 0.920
M 12 1.75 12.000 10.863 10.106 9.858 1.074
M 14 2 14.000 12.701 11.835 11.564 1.227
M 16 2 16.000 14.701 13.895 13.454 1.227
M 18 2.5 18.000 16.376 15.294 14.933 1.534
M 20 2.5 20.000 18.376 17.294 16.933 1.534
M 24 3 24.000 22.051 20.752 20.320 1.840
M 30 3.5 30.000 27.727 26.211 25.706 2.147
M 36 4 36.000 33.402 31.670 31.093 2.454
M 45 4.5 45.000 42.077 40.129 39.416 2.760
M 52 5 52.000 48.752 46.587 45.795 3.067
M 60 5.5 60.000 56.428 54.046 53.177 3.374

5. 55

Screw Threads
Nuts and Bolts Table 3.2
d
c
(mm)
Designation P (mm)
D or,
D (mm)
d
p
(mm)
Nut Screw
Thread Depth
(mm)
M 8 × 1 1 8.000 7.350 6.918 6.773 0.613
M 10 × 1.25 1.25 10.000 9.188 8.647 8.446 0.767
M 12 × 1.25 1.25 12.000 11.184 10.647 10.466 0.767
M 14 × 1.5 1.5 14.000 13.026 12.376 12.166 0.920
M 16 × 1.5 1.5 16.000 15.026 14.376 14.160 0.920
M 18 × 1.5 1.5 18.000 17.026 16.376 16.160 0.920
M 20 × 1.5 1.5 20.000 19.026 18.376 18.160 0.920
M 22 × 1.5 1.5 22.000 21.026 20.376 20.160 0.920
M 24 × 2 2 24.000 22.701 21.835 24.546 1.227
M 27 × 2 2 27.000 25.701 24.835 24.546 1.227
M 30 × 2 2 30.000 28.701 27.835 27.546 1.227
M 33 × 2 2 33.000 31.701 30.335 30.546 1.227
M 36 × 3 3 36.000 34.051 32.752 32.391 1.840
M 39 × 3 3 39.000 37.051 35.752 35.391 1.840
Note : See the Tables 3.1 and 3.2 at the end of this unit.
3.4 RIGHT AND LEFT HAND THREADS
When a nut is rotated in clockwise direction looking along axis from the nut and nut
advances on the thread, the thread is right hand. For similar advance and looking at nut
axially if nut rotates anticlockwise then the thread is left hand. Figure 3.4(a) shows right
hand thread. Figure 3.4 compares right hand and left hand threads.

(a) (b)
Figure 3.4
3.5 SINGLE AND MULTIPLE START THREADS
A single threaded screw contains only one helix running on a cylindrical surface.
Naturally there will be only one end from where the thread starts, hence it is called single
start thread. There may be two or more helixes running parallel on the cylindrical surface.
They will start from as many ends. Such threads are called multi start threads. The nut on
a single start thread will advance a distance equal to pitch in one rotation. In double or
triple start thread the nut will advance by two or three pitches in one rotation. The nut
advance per rotation is called lead. Figure 3.5 shows single start and double start threads.

Figure 3.5

6. 56
Machine Drawing SAQ 1
Draw external thread and internal thread profiles for
(a) M52
(b) M30
(c) M39 ×3
Consult Tables 3.1 and 3.2.




3.6 THREAD PROFILE TYPES
V-Threads
It must be first understood that threaded screws are used for two purposes. They
are (a) fastening (b) power transmission. The thread profiles for fasteners is such
that the flanks make an acute angle at thread tip while the power screws have
threads with flanks parallel or near parallel. Common thread profiles are
described below.
3.6.1 Sharp V- Thread
The ISO V-thread, already described in Section 3.3 and Figure 3.2 are most popular in
use in fastener. Sharp V-threads have almost same profile with tips not removed.
Although the flank areas are larger than in ISO thread, yet the strength is limited because
of sharp region at the top of threads. This thread is used in brass pipes. They are difficult
to make as the sharp portion tend to be damaged. Figure 3.6(a) shows this thread form.
3.6.2 Whitworth Standard Thread
This V- thread is much similar to ISO standard thread with such differences as flank
angle is 55
o
instead of 60
o
. The other differences can be seen in Figure 3.6(b). This form
was earlier used in Great Britain and also in India. They are often referred to as BSW.
3.6.3 British Association Thread
Called B. A thread, they again resemble the form of ISO or BSW threads but the flank
angle is 47.5
o
. The crests and roots are rounded.
Sharp V-threads, BSW threads and B.A threads are shown in Figures 3.6(a), (b) and (c)
respectively.

(a) Sharp V – Thread

7. 57

Screw Threads
Nuts and Bolts

(b) British Standard Whitworth Thread (B. S. W.)

(c) British Association Thread (B. A.)
Figure 3.6 : Three Thread Forms
3.6.4 American National Thread
Commonly used in USA, these threads differ with ISO profile in that they have flat crests
and roots. They are general purpose for fasteners such as bolts and nuts, screws and
tapped holes. Figure 3.7(a) depicts this form.
3.6.5 Unified Standard Thread
These V-threads used in fasteners are popular in U.S.A, Canada and Britain. The flank
angle is 60
o
with rounded crests and roots as shown in Figure 3.7(b). The shapes of the
crests and roots are different in internal and external threads.

(a) American National Standard Thread

(b) Unified Standard Thread
Figure 3.7

8. 58
Machine Drawing
3.7 SQUARE, ACME AND BUTTRESS THREADS
These threads are used in screws that are meant for power transmission rather than
fastening. For power transmission it is essential that frictional torque must be less and it
is achieved with Square, Acme or Buttress threads.
In square threads as shown in Figure 3.8(a) the flanks are parallel. The outer or larger
diameter is called major diameter and minimum diameter is called the core diameter. The
pitch diameter is not defined for square threads as over the entire depth the thickness of
the thread is same. Instead a mean diameter is defined as mean of major and core
diameter.

(a)

(b)
Figure 3.8 : Profile of Square Thread and Proportions
Acme thread and Buttress threads as shown in Figures 3.9(a) and (b) are other variations.

(a) Acme Thread Profile

(b) Buttress Thread
Figure 3.9

9. 59

Screw Threads
Nuts and Bolts SAQ 2
The pitch of 10 mm can be used for core diameters of 55, 58 or 72 mm, and
corresponding major diameters of 65, 68 and 82 mm are permissible. Draw profiles
of Square, Acme and Buttress threads.





3.8 REPRESENTATION OF THREADS
Screw threads are shown by some conventional method on drawing. Showing threads in
their helical form and actual shape (see Figure 3.1) will be difficult and time consuming.
For external threads continuous thick lines are used to show the crests of the thread. The
roots are represented by continuous thin lines. The hidden or internal threads are depicted
by medium broken lines. If the threaded part is sectioned then hatching extends to the
line representing the crest. In the end or side view the roots are represented by part of a
circle of diameter equal to core diameter. Three fourths of the circle is drawn.

(a) Schematic Representation of External Thread, Elevation
(b) Schematic of External Threads,
(c) and (d) End Views

(e) Convention to show Some Details of Thread
Figure 3.10

Yet other practice is to draw thread lines, thin lines to join the crest lines across and thick
lines to join root lines. The external threads are represented in this way without
sectioning the part but internal threads are thus shown only when sectioned. In the latter
case the section hatching lines will extend to only the line of roots which will now be
drawn thick, (see Figures 3.10 and 3.11).

10. 60
Machine Drawing

Figure 3.11 : Schematic of Internal Threads (a) Without Sectioning, Elevation,
(b) End View, (c) With Section, Elevation, (d) Another convention for Internal Thread with
Greater Details

In case of square threads the actual threads are shown in large size drawings.
SAQ 3
(a) Standard ISO threads M10 are turned on a bar of 15 mm diameter. Show
the threads by two convention with and without section.
(b) The same threads are turned inside, show them by two conventions with
and without section.
(c) Square threads of 6 mm pitch are turned on a bar of 32 mm diameter.
Show conventional representation with part of bar unthreaded.




3.9 NUT AND BOLT
A bolt is cylindrical in shape and it has two distinct shapes in continuous body. The head,
formed by upset forging, is normally hexagonal or square and integral with threaded
cylindrical body called shank. The nut is rotated on the threads of the bolt shank by the
help of a spanner as shown in Figure 3.12. The hexagonal head apparently helps
tightening by rotating over small angles. Many times another spanner may be used to
hold the bolt head so that the combination of nut and bolt does not rotate as a unit. The
wrench or spanner holds the hexagon on two parallel faces. The square nut or bolt head
also provides two parallel faces to be held by the spanner but hexagonal shape is
preferred because it is stronger than square shape for same amount of metal. Figure 3.13
represents a bolted joint.

Figure 3.12 : A Wrench Tightening A Bolt

11. 61

Screw Threads
Nuts and Bolts
A
B
C
D
E
F
G
H
A’
B’
E’
F’
A’ B’ G’ D’ E’ F’ C’

Figure 3.13 : A Bolted Joint
3.10 SHAPE OF BOLT HEAD AND NUT
A hexagonal head of a bolt or a nut will appear like what is shown in Figure 3.14. Of
course, the shape of both has already been drawn in Figure 3.13.






Figure 3.14
A hexagon or even a cylinder will end in sharp edges which are chamfered. The
hexagonal head is chamfered along 30
o
creating a circle inscribed inside the regular
hexagon.
The inscribed circle is tangential to all sides of the regular hexagon. The part of surface
between the inscribed circle which is called chamfer circle is slightly complicated to
draw on paper.
We will develop an under standing to draw the details. From the top view if front view is
to be developed we can easily see the correspondence between A and A′, B and B′, C and
C′ and D and D′ .
Note all the points A, B, C and D below the top surface because of chamfering. So in the
front view we see the head between the corners with points A, B, C and D placed at same
level but below the top surface. The points E and G are at top level but AE is inclined at
30
o
to horizontal, (30
o
is angle of chamfer). Note E will be visible as E′ in front view.
E to G (if there is no hole) or EHG will appear as straight line which will coincide with
EFG appearing as E′ F′ G′. But points B′ and C′ will appear below the line of E′ F′ G′.
A′ B′ will be a curve and similarly B′ F′ C′ will be another curve. It is difficult to identify
these curves but they are conveniently assumed as parts of circles.
In the end view F will appear as F′ and E will appear as E′ – both at top surface but A and
B will project as A′and B′ at lower level. This (end) view is the view between the flats of
the head or nut. The curve between A′ and B′ is difficult to identify but is drawn as part of
a circle.
As is the practice with all engineering products, the nuts and bolts are also standardized.
However, due to the frequency of replacement the nuts and bolts are marked with much

12. 62
Machine Drawing greater degree of standardization in terms of dimensions, materials, heat treatment and
manufacturing. In the present context of drawing we are concerned only with the
standard dimensions and others may be seen and understood at the proper stage.
From the Figure 3.13 it appears that the diameter of the hole in the nut or diameter of the
shank is equal to the side of the regular polygon or the width of the face. In that case the
width of the nut will be 1.73d and distance across the corners will be 2d. But for
convenience of drawing following proportions are adopted.
The major bolt diameters – d
Thickness of the nut – d
Thickness of the bolt head, – 0.75 d, Thickness of the nut – d
Width across flat surfaces – 1.5 d + 3 mm
Radius of the chamfer arc in elevation, R, – 1.5d
3.11 PROCEDURE OF DRAWING
Let us take the example of a nut of major diameter d = 32 mm.
(a) Draw the top view by drawing a circle of diameter, d and another circle of
diameter 1.5d + 3 mm. On the bigger circle draw a regular polygon with two
horizontal sides.
(b) As explained earlier project the front view and obtain points like A′, B′, C′,
and D′. The positions of these points are such that all of them lie on same
horizontal line. E in top view is projected to E′. A line is drawn from E′ at
30
o
to horizontal. This inclined line intersects the vertical line through A
at A′. Similarly D′ on vertical line through D is obtained. A′ D′ is a horizontal
line giving points B′and C′ .
(c) On the centre line choose the center O
1 at a radius of R = 1.5d 1 and draw the
chamfer arc between B′and C′.
(d) Assuming C′ and D′ to lie on the same arc of a circle locate the center of the
circle at O
2, which will lie on intersection of perpendicular bisectors of D′ K
and C′ K. K is on the top line of the front view between C′ and D′.
(e) With O
2 as center and O 2 K as radius draw the arc C′ K D′. The point G
1
will
marginally above this arc. Similarly draw the arc between A′ and B′. Both E′
and G′ are above these arcs respectively.
(f) Draw a horizontal line between E′ and G′ and join E′ with A′ and D′ with G′.
(g) For end view project end view (third angle in this case) to the right noting
that points J and K project to positions J′ and K′ respectively higher than the
positions C′, B′ and H′ , I′ where corresponding projections from front view
have been obtained. Thus entire end nut view is rectangle divided in the
middle.
(h) Join C′, D′ and H′ with a horizontal line and note that C′ and D′ lie on a
circle which represents the chamfer. Similarly D′ and H′

lie on a circular arc.
(i) Geometrically determine the centers O
3 and O 4 for circular arcs between C′,
D′ and between D′ and H′.
(j) Draw the arcs in the view with radius R
1.
The entire procedure is illustrated in Figure 3.15

13. 63

Screw Threads
Nuts and Bolts











Figure 3.15 : Procedure for Drawing Nut of A Bolt
Figure 3.16 illustrate drawing of views of bolt head (first angle projection in this case).
The drawing is self illustrative. For distinction major diameter of thread on bolt is
denoted by D⋅ A/F denotes distance between flat faces. The procedure involves locating
points E′ and G′ from plan establishing radius R
1.

Figure 3.16 : Procedure for Drawing Front View of Bolt Head. Stage I
Shows the Construction and Stage II shows Completed Drawing
Then draw a circle of radius R
1 and with center C 1 and locate center C 2. Then draw
another circle with center C
2 and radius and locate center C 3. C3 is used as center with
radius A/F to draw the arc in the center between the vertical lines representing corners in
the front view. The centers C
4 and C 5 are located as intersections of two circles drawn
earlier. Hence the view is completed. The side view is drawn in the same way as
described in respect of Figure 3.15.
3.12 DRAWING COMPLETE BOLT
A bolt with head, length with and without threading and end is shown in Figure 3.17. The
threaded portion is drawn as per rule already described in last unit. Two alternatives for
finishing ends – one as done and either as flat chamfered are shown in Figure 3.17. Note
that the chamfer angle is 45
o
. Also not the run out of the threads as the entire length of
bolt shank is not threaded. Thread lengths of different magnitudes are provided by
manufacturers.
A
B J C
D
I H K
E G
A
’
B
’
C
’
D
’
E J’K’ G

14. 64
Machine Drawing

Figure 3.17 : A Complete Bolt
3.13 SQUARE HEADED BOLT AND SQUARE NUT
The dimensions for square head or square nut are :
Thickness – d
Width of the nut – 1.5 d + 3 mm
Radius of chamfer arc – 2d
The procedure of drawing very much follows the steps already described and now
illustrated in Figure 3.18.
Two types of projections can be drawn depending upon placement of top view. The
auxiliary view shown to the right of front view can become front view if the plan is
rotated by 45
o
. The radius R can be seen, through geometrical construction, to be equal to
the depth or major thread diameter. In the other view it is 2d.

Figure 3.18 : Drawing Square Nut or Head of a Bolt
SAQ 4
(a) Two 8 mm thick plates are bolted by passing the 10 mm major diameter bolt
through 11 mm diameter hole. The nut is tightened on top. Draw the
dimensioned front view.
(b) Schematically show external and internal thread in engagement creating a
joint.
(c) Bolts of hexagonal head and square head have shank lengths of 4D each and
threaded over half the length. Draw front views along the length (length in
full) and end views.

15. 65

Screw Threads
Nuts and Bolts
Stud end

Plain Nut end
3.14 WASHER
Washers are used between the nut and the flat surface of the part tightened by the bolt.
Apparently the shank of the bolt must pass through the washer. For this reason washer is
a thin ring (0.15 d thick) with an inner hole of diameter just 1 mm greater than the bolt
diameter. The outer diameter is greater than the distance between the corners of the nut
by 4 mm. The washer serves to distribute the force between the under side of the nut and
the surface of the jointed parts uniformly and even some roughness or unevenness is
tolerable in the presence of the washer. Figure 3.19(a) shows a washer and Figure 3.19(b)
shows a washer and nut.

(a) A Washer (b) A Washer With N ut
Figure 3.19
3.15 STUD
Stud is like a shank (bolt without head) threaded on both ends. It is used in a joint in
which one member is very thick so that the bolt does not come out at the other end. The
threads are made by tapping in the thicker part in which taps of increasing number of
threads are run in drilled blind holes. The studs are also used in places where bolt head is
obstructed before reaching the hole. The other end of the stud is tightened with a nut
normally placed upon a washer. A stud and a studded joint are shown in Figure 3.20.











(a) Stud (b) Studded Joint

Figure 3.20
3.16 EYE BOLT
An eye bolt is fitted into heavy bodies of machine to lift them by cranes or winches.
Figure 3.21(a) shows a gear drive whose upper half is fitted with eye bolts for lifting
cover. Many machines are, likewise, fitted with eye bolts.

16. 66
Machine Drawing
Bearing Cover
Hook
Hook
Eye bolt

Figure 3.21(a) : Eye Bolts Fitted to Gear Drive Cover for Lifting

Figure 3.21(b) : Eye Bolt Dimensions
Eye bolt dimensions are described in terms of major thread diameter which is calculated
on the basis of the load to be lifted.
3.17 OTHER BOLT HEADS
Several types of heads for bolts are used, though the hexagonal and square heads
dominate. The other bolts are used to serve special purpose. Here, we confine to show the
bolt heads in Figures only. D in following figures represents major thread diameter.

Figure 3.22

17. 67

Screw Threads
Nuts and Bolts

Figure 3.23

Figure 3.24

Figure 3.25

Figure 3.26

18. 68
Machine Drawing

Figure 3.27

Figure 3.28

Figure 3.29
3.18 OTHER NUT SHAPES
Lock nuts are used below the main nut which has one end chamfered and other end flat.
The lock nut has both ends chamfered. They prevent the main nut from loosening.
Figure 3.30 shows a lock nut. Flanged nut shown in Figure 3.31 carry its washer and
distributes force over larger area, thus reducing pressure. Cap nut Figure 3.32 and dome
nut Figure 3.33 do not allow the dust, etc. enter the threaded region.

19. 69

Screw Threads
Nuts and Bolts

Figure 3.30

Figure 3.31

Figure 3.32 : Cap Nut

Figure 3.33 : Dome Nut

20. 70
Machine Drawing SAQ 5
Draw a bolted joint in section (front view), between circumference of a cylinder
and cover. Cylinder diameter = 400 mm. Number of bolts = 12. Pitch circle
diameter of bolts = 480. M 20 bolt with d = 20 mm, p = 2.5 mm and d
1 = 17.3 mm
is to be used. The bolt is inserted from below and nut with washer is used from top.








3.19 SUMMARY
Threads of different types like V-square, acme and buttress threads have been described.
Several standards of V-threads were introduced. ISO form of the thread is most
acceptable, yet BSW, BA, American National and unified standard threads are in use.
Threads are often shown on drawings in schematic ways. Schemes of representing V-
threads and square threads have been introduced with an idea to reduce confusion and
difficulty in drawing.
The bolts and nuts are threaded parts used to create bolted joints between parts of
structure the shapes and dimensions of both are standardized. Studs are threaded
cylindrical pieces which do not have heads and do not pass through the thickness. Two
types of bolt heads commonly used are hexagon and square. Washers are used to
distribute force between underside of nut and the surface in contact. For keeping nut is
position the washer may help but look nut is often used.
An eye bolt is like a fall hook with threaded cylindrical part on one side. It is used for
lifting heavy machine parts.
3.20 ANSWERS TO SAQs
SAQ 1
(a) M 52 is coarse thread and from Table 3.1
d = 52 mm, d
c = 46.587 mm, d p = 48.75 mm, p = 5.0 mm
H = 0.866025 × p
= 0.866025 × 5.0 = 4.33 mm
Refer to Figure
0.25 H = 0.25 × 4.33 = 1.0825 mm
0.167 H = 0.167 × 4.33 = 0.723 mm
0.125 H = 0.125 × 4.33 = 0.54 mm
The external threads are drawn in Figure 3.34 and the internal threads in
Figure 3.35.

21. 71

Screw Threads
Nuts and Bolts
0.54
60
o
1.08

52
48.75
46.587
















Figure 3.34 : External Thread















Figure 3.35 : Internal Thread
SAQ 2
For Square thread : Depth of thread
10
5mm
2 2
p
= = =
Width of thread 5 mm
2
= =
p

Distance between flanks 5 mm
2
= =
p

0.54
0.54
5.0
60
o
0.723 R

0.723
1.08

4.33
52
48.75
46.587
2.5

22. 72
Machine Drawing
15φ
2R M10 × 1.5
4
20
1.5
2R M10 × 1.5
For Acme thread : Depth of thread 0.25 5.25 mm
2
= + =
p

Angle θ = 15
o

Width of thread at crest = 0.37 p = 3.7 mm
For Buttress thread : Depth of thread = 0.503 p = 0.503 × 10 =5.03 mm
Angle between flanks = 45
o

Also see Figure 3.35
The profiles are drawn in Figure 3.36.





(a) Square Thread






(b) Acme Thread






(c) Buttress Thread
Figure 3.36
SAQ 3
(a)





(a) Conventional Schematic of Thread




(b) Sectional Schematic of Thread
3.7 3.7
10
15
O
54.5 59.75 65.5
45
O
10

65

59.75

54.94

1.4

5.03

8.9

5 5
5
55 60 65

23. 73
Screw Threads
Nuts and Bolts
M 10 × 1.5
20 φ 20 φ
20 φ
(a) (b) (c) (d)
Front view Front view End view
Plain
2R
4
1.5
1.5
10φ





(c) Second Type of Thread Schematic without Sectioning
Figure 3.37
(b)





(a) Conventional Representation of Internal Threads without Sectioning
(b) Conventional Section Representation of Internal Threads,
(c) Another Conventional Representation of Internal Threads
(d) End View of Internal Threads
Figure 3.38
(c) P = 6 mm, d = 32 mm, d
1 = d – p = 32 – 6 = 26 mm,

1
32 26
29 mm
2 2
+ +
= = =
m
d d
d

6
tan 0.658
29
α = = =
π π ×
m
p
d
, α = 3.77 degree.








Figure 3.39 : Schematic of Square Threads, Elevation and End View
SAQ 4
Answers are depicted respectively in Figure 3.40, Figure 3.41 and in
Figures 3.42(a) and (b).









Figure 3.40
3
3
26 φ 32 φ
3 6
3.77
o

24. 74
Machine Drawing
30
o
30
o
30
o
R 270

R 240

R
200

20
18 30
30
12 M 20 Bolts






Figure 3.41


(a) Hexagonal Head Bolt (b) Square Head Bolt
Figure 3.42
SAQ 5

















Figure 3.43