Threads

(1)

Threads and

Fasteners

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Fastening – What is it?

•• A method of connecting or joining two

A method of connecting or joining two

or more parts together, using devices or

processes.

•• Examples: Bridges, towers, buildings,

Examples: Bridges, towers, buildings,

transportation, piping, sports, etc.

(3)

Threaded Fasteners

•• A mechanical fasteners used to join

A mechanical fasteners used to join

together two or more parts.

•• Are formed by using a tapping tool for

Are formed by using a tapping tool for

internal threads, a die for external

threads, or a machine tool for either

internal or external threads.

(4)

Applications

•• There are 3 major types of Threaded

There are 3 major types of Threaded

Fastener Applications, they are:

–

– Joining

Joining

–

– Adjusting

Adjusting

–

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Adjusting

•• The process of locating or modifying

The process of locating or modifying

the position of a part.

•• Examples: Drafting Compass – uses a

Examples: Drafting Compass – uses a

threaded rod to adjust the radial setting.

•• Calipers, micrometers, hand wrenches,

Calipers, micrometers, hand wrenches,

etc.

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Power Transmission

•• The process of converting or

The process of converting or transmitting

transmitting

the force exerted in one direction to force

exerted in the same or a different

direction.

•• Screw Jacks and certain types of gears

Screw Jacks and certain types of gears use

use

screw threads to transmit power.

•• Good example of this

Good example of this

is a Car lift

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External (male)

thread

Internal (female)

thread

THREAD TERMINOLOGY

A thread cut on the

A thread cut on the outsideoutside of of a cylindrical body.

a cylindrical body. A thread cut on the

A thread cut on the insideinside of of a cylindrical body. a cylindrical body. Internal thread Internal thread External thread External thread

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Right-hand

thread

Thread that will

Thread that will assembleassemble whenwhen turned

turned clockwiseclockwise..

Left-hand

thread

Thread that will

Thread that will assembleassemble whenwhen turned

turned counter-clockwisecounter-clockwise..

THREAD TERMINOLOGY

Turnbuckle

Turnbuckle use RH and LH thread atuse RH and LH thread at

each end to double displacement.

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Crest

Root

Thread angle

THREAD TERMINOLOGY

The

The peak edge peak edge of a thread.of a thread. The

The bottombottom of the thread cut intoof the thread cut into a cylindrical body.

a cylindrical body.

The angle between threads faces. The angle between threads faces.

Internal Thread Internal Thread External Thread External Thread Crest Crest Root Root Thread angle Thread angle Crest Crest Root Root

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Major diameter

TheThe largest diameter largest diameter onon

an internal or external thread. an internal or external thread.

Minor diameter

TheThe smallest diameter smallest diameter onon

an internal or external thread. an internal or external thread.

Internal Thread Internal Thread External Thread External Thread M M i

i n n o o

r

d

i

i a a . .

M M a a j j o o r r d d i

i a a . .

THREAD TERMINOLOGY

M

i

i n n o o

r

d

i

i a a . .

M M a a j j o o r r d d i

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Form is the profile shape of t Form is the profile shape of thehe thread. thread.

Thread Form

THREAD TERMINOLOGY

Example Example ::

“knuckle thread form” “knuckle thread form”

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COMPARISON OF THREAD CUTTING

External Thread

_{Internal Thread}

Major Dia. Major Dia.

Minor Dia. Minor Dia.

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EXTERNAL THREAD CUTTING

Tools

_Operation

Threading Die Threading Die

Die stock Die stock

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Tools

Tap Tap Tap wrench Tap wrench

Operation

INTERNAL THREAD CUTTING

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Pitch Pitch

DEFINITION OF SCREW

THREAD TERMS

•• TheThe pitch pitch of a thread isof a thread is the distance from one the distance from one point on the thread form to point on the thread form to the corresponding point of the corresponding point of the

the next next thread. thread. Pitch Pitch isis measured parallel to the measured parallel to the thread's axis or centerline. thread's axis or centerline.

Click to see a sample Click to see a sample appear to the right

appear to the right

Pitch Pitch Notice the Notice the pitch can be pitch can be measured measured from from crest-to-crest crest OROR Root-to-Root Root-to-Root

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Pitch

The distance between crests of The distance between crests of

threads. threads.

Lead

The distance a screw will advanceThe distance a screw will advance

when turned 360 when turned 360oo_..

THREAD TERMINOLOGY

Internal Thread Internal Thread External Thread External Thread Pitch Pitch Pitch Pitch

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DEFINITION OF SCREW

THREAD TERMS

•• The

The lead

lead (pronounced "leed") is the distance

(pronounced "leed") is the distance

that a threaded part (such as a nut) would

move or travel in the horizontal direction if the

screw thread was rotated 360 degrees.

•• Threads are always assumed to be

Threads are always assumed to be right

right

handed

handed threads

threads unless marked with the

unless marked with the

initials

initials LH

LH (Left Hand)

(Left Hand) at the end of the thread

at the end of the thread

note.

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SINGLE AND MULTIPLE THREADS

••

Most screws Most screws have singhave single threads. le threads. Assume single Assume single thread unlethread unless otherwisess otherwise noted. Multiple threads are used where parts must screw together or apart noted. Multiple threads are used where parts must screw together or apart quickly. For example, the compass adjustment bar and toothpaste tube caps quickly. For example, the compass adjustment bar and toothpaste tube caps have multip

have multiple threads. le threads. Notice in Notice in the picture the picture above thaabove that:t:

–

– Single Thread - The lead is equal to the pitch.Single Thread - The lead is equal to the pitch. –

– Double Thread - The lead is twice the pitchDouble Thread - The lead is twice the pitch –

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Single and

multiple threads



A single thread has a

single ridge in the form

of a helix.



A double thread has two

ridges started 180

° °

apart.



A triple thread has three

ridges, started 120

° °

apart.

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THREAD SERIES

•• Screws Screws of of the the samesame diameter are made with diameter are made with different pitches (number different pitches (number of threads per inch) for of threads per inch) for different uses. The various different uses. The various combinations of diameter combinations of diameter

and pitch have been

grouped into

grouped into screw-thread screw-thread series

series..

•• Coarse-thread Series (UNC or NC Coarse-thread Series (UNC or NC )) InIn this series the pitch for each diameter is this series the pitch for each diameter is relatively large.

relatively large.

•• Fine-thread Series (UNF or NF)Fine-thread Series (UNF or NF) In thisIn this series, the pitch for each diameter is series, the pitch for each diameter is smaller (there are more threads per inch) smaller (there are more threads per inch) than in the coarse- thread series. than in the coarse- thread series. Example automobiles

Example automobiles

•• Extra-fine-thread Series (UNEF Extra-fine-thread Series (UNEF or or NEF)

NEF) In this series, the pitch is evenIn this series, the pitch is even smaller than in the fine-thread series. smaller than in the fine-thread series. Example airplanes and gears

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CLASSES OF FITS

•• Screw Screw threads threads are are alsoalso divided into

divided into screw threascrew threa classes

classes based based on on their their tolerances

tolerances (amount of size(amount of size different from exact size) and different from exact size) and allowances

allowances (how loosely or (how loosely or tightly they fit their mating tightly they fit their mating parts). You can get exactly parts). You can get exactly the screw thread you need by the screw thread you need by choosing both a series and a choosing both a series and a class. In brief, the classes for class. In brief, the classes for Unified threads are:

Unified threads are:

•• Class 1Class 1 has a large allowancehas a large allowance (loose fit). They are used on (loose fit). They are used on parts that must be put together or parts that must be put together or taken apart quickly and easily.

taken apart quickly and easily. •• Class 2 Class 2 is the thread standardsis the thread standards

most used for general purposes, most used for general purposes, such as for bolts, screws, nuts, such as for bolts, screws, nuts, and similar threaded items.

and similar threaded items.

•• Class 3Class 3 has stricter standards for has stricter standards for fit and tolerance than the others. fit and tolerance than the others. They are used where thread size They are used where thread size must be more exact. Simply, a must be more exact. Simply, a tighter fitting thread.

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“A” Or “B”

•• The letter The letter “A”“A” following the fit class number (1,2, or following the fit class number (1,2, or 3) denotes

3) denotes external threadsexternal threads only;only;

•• the letter the letter “B”“B” following the fit class number denotesfollowing the fit class number denotes internal threads

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READING A THREAD NOTE

T

Thhrreeaad d NNoottee DDeeffiinniittiioon n oof f MMeeaanniinngg .750

.750 0.750 diameter (3/4”)0.750 diameter (3/4”) 10

10 10 threads per inch10 threads per inch U

UNNCC UUnifiednified NNationalational C

Coarse thread seriesoarse thread series 2

2 Class 2 (Normal Fit)Class 2 (Normal Fit) A

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READING A THREAD NOTE

•• You specifyYou specify (call for) a particular (call for) a particular screw thread by telling its screw thread by telling its diameter (nominal or major diameter (nominal or major diameter), number of threads per diameter), number of threads per inch, length of thread, initial inch, length of thread, initial letters of the series, and class of letters of the series, and class of fit. Any thread you specify will be fit. Any thread you specify will be assumed to be both single and assumed to be both single and right hand unless you say right hand unless you say otherwise. If you mean the thread otherwise. If you mean the thread to be left hand, include the letters to be left hand, include the letters “LH” after the class symbol. If you “LH” after the class symbol. If you mean it to be double or triple, mean it to be double or triple, include "double" or "triple." Some include "double" or "triple." Some examples using fractional sizes examples using fractional sizes follow:

follow:

•• 1 1/4-7UNC-1A1 1/4-7UNC-1A

Means 1 ¼” diameter, 7 Means 1 ¼” diameter, 7 threads per inch, Unified threads per inch, Unified National Course threads, National Course threads, class 1 fit, external threads. class 1 fit, external threads. •• 7/8-14UNF-2B7/8-14UNF-2B

Means 7/8” diameter, 14 Means 7/8” diameter, 14 threads per inch, Unified threads per inch, Unified

National Fine threads, class National Fine threads, class 2 fit, internal threads

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1.

1. 1. Detailed

Detailed representation

Detailed

representation

2.

2. 2. Schematic

Schematic representation

Schematic

representation

3.

3. 3. Simplified

Simplified representation

Simplified

representation

THREAD REPRESENTATION

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External thread

Internal thread

DETAILED

REPRESENTATION

60

60oo

Pitch

Use

Use slanting linesslanting lines to represent crest and root.to represent crest and root. Roots and crest are drawn in

Roots and crest are drawn in sharpsharp Vs.Vs.

Thread runout

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SCHEMATIC

REPRESENTATION

External thread

Pitch

Pitch _{Crest (thin line)}_{Crest (thin line)}

Root (thick line) Root (thick line)

Use alternate

Use alternate long long andand short short lines for representinglines for representing crests

crests andand rootsroots of the thread, of the thread, respectively.respectively.

Internal thread

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BOLT :

Terminology

Bolt

Bolt is a threaded cylinder with a head.is a threaded cylinder with a head.

Hexagonal head

bolt and nut

bolt and nut _thickness_thicknessHeadHead

Thread length Thread length Length Length Width Width across flat across flat

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Bolt measurements

(30)

Draw Draw bolt bolt axis axis Draw an Draw an end view end view of the head of the head B B Starting Starting position position H H Draw a Draw a bolt head bolt head B/2 B/2 B/2B/2 30 30oo Length Length Thread Length Thread Length M M a a j j o o r r φ φ Draw Draw body of a bolt body of a bolt