ME 114 – Engineering Drawing II

Dr. A. Tolga BozdanaAssistant Professor

Mechanical EngineeringUniversity of Gaziantep

SCREW THREADS, BOLTS and NUTS

1

Threaded FastenersThread is the helical grooves which are opened to inner and outer surfaces. Fig. 1shows the screw thread terminology.

External thread (screw/vida - bolt/cıvata -stud/saplama): A thread on the external surface of a cylinder.Internal thread (nut/somun): A thread on the internal surface of a cylinder.

Major diameter (diş üstü çap): The largest diameter of a screw thread.

Minor diameter (diş dibi çap): The smallest diameter of a screw thread.

Pitch 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

2

Threaded FastenersCrest: 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 thread: The distance between crest and root measured normal to the axis.

Pitch (hatve, adım): 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

3

Threaded FastenersLead: 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

4

Screw Thread Profiles

Figure 3

Profiles of standard screw thread forms used in industry are shown in Fig. 3.

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-LHa b c d e

a: Major diameter (inch)b: Threads per inchc: Form (i.e. Unified National Coarse)d: External thread (B for internal)e: Left-hand thread (RH for right-hand)

British Type Metric TypeM20 x 2x y z

x: Metric screw thready: Major diameter (mm)z: Pitch (mm)

Figure 5

Figure 4

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

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 BoltFigure 10

8

Assembly Drawings of Bolted and Stud Joints

tabulatedtabulated

4.05.0

25.15.2 to2

tabulated3

5.0on based

5.12 to

15.01.1

2.27.08.0

285.0

diametermajor

13

12

1

0

2

1

==

+=+=

===========

=====

nm

dlldll

dlddl

ldK

cRRr

dRssc

dsdA

dDdhdH

dDdd

d

w

Figure 12 Bolted Joint Figure 13 Stud Joint

d1d

c

Hs

nm

h

D

A

R l0l

KDw

R2

r

d1d

Hs

nm

l0l

KDw

A

l1

l2l3

D

R rc

9

Various Types of Bolts and Nuts

Figure 14

Figure 15